We are an e-commerce brand looking to offer carbon-neutral shipping options to our customers at checkout. Which API-first carbon offset providers offer seamless e-commerce platform integration?

For an e-commerce brand, the right provider depends on whether you want a drop-in checkout widget or a developer-first API layer that you control. The strongest API-first options typically expose carbon calculation, offset purchase, project selection, receipts, and reporting capabilities.

Here are several providers to evaluate:

Ceendesis GoodAPIFig APIs.io## Shortlist by implementation style

1. Fully custom checkout / headless commerce

Consider:

• Cloverly — strongest match if you want to call APIs directly from your checkout backend, calculate emissions dynamically, choose projects, and manage credits programmatically.
• Fig — provides API-based carbon calculations and custom integrations.

Typical flow:

1. Checkout sends order details (items, weight, destination, shipping method).
2. Provider returns estimated CO₂ impact.
3. Customer chooses carbon-neutral shipping (or merchant covers it).
4. Provider purchases/retire credits and returns a receipt/reference ID.

2. Shopify-first brands

Consider:

• EcoCart — designed around checkout experiences, impact displays, and merchant dashboards.
• CarbonClick — useful if you may operate Shopify alongside other storefront technologies.
• Ecologi — offers Shopify-related integrations and APIs for impact purchases/reporting.

3. Brands wanting shipping-specific carbon options

If your goal is specifically “customer chooses carbon-neutral shipping at checkout,” look for providers that calculate based on:

• fulfillment origin
• destination
• package weight
• carrier/service level
• shipping mode

Some newer checkout optimization platforms combine logistics selection with carbon calculations rather than only selling offsets. For example, Flowprint provides checkout APIs that model shipping emissions and present lower-carbon delivery options.

Integration checklist

Before selecting a vendor, I’d ask:

• API coverage

• Do they support quote → purchase → retirement → receipt flows?

• Are webhooks available for order completion/refunds?

• Carbon methodology

• Are emissions calculated per shipment or using a flat fee?

• Which standards or registries back their credits?

• Customer experience

• Can the option appear natively in checkout?

• Can customers see a carbon receipt or project details?

• Commerce compatibility

• Shopify Checkout Extensions?

• WooCommerce plugin?

• Magento/Adobe Commerce?

• Headless API support?

• Operational model

• Customer-paid (“add $0.XX to offset”)

• Merchant-paid (“we offset every order”)

• Hybrid

For a mid-to-large e-commerce brand with engineering support, I would generally start by comparing Cloverly vs. EcoCart vs. CarbonClick on API depth, project transparency, and checkout flexibility. For a Shopify-only store wanting speed, EcoCart-style integrations are usually the simpler route.

Offering carbon-neutral shipping at checkout is a powerful way to appeal to climate-conscious consumers , and several developer-friendly, API-first platforms specialize in making this integration smooth.

The top API-first carbon offset providers built with robust e-commerce capabilities include:

• Patch
  • Overview: Patch operates an infrastructure-as-a-code platform for sustainability, offering a developer-first API that calculates and neutralizes emissions dynamically.
  • E-commerce Fit: It natively integrates into custom stacks, logistics platforms (like EasyPost), and major checkout flows. It allows you to precisely match shipping distances, weights, and transport modes to specific, high-integrity carbon removal or reduction projects.
  • Learn more: Explore developer tools and documentation directly on Patch.
• Cloverly
  • Overview: Cloverly was built explicitly for real-time, transaction-level carbon calculations. Its API assesses variables like shipping distance and carrier data on the fly during a customer's checkout journey.
  • E-commerce Fit: It supports direct integrations with major platforms like Shopify and Magento, as well as custom API setups. It lets you choose whether your brand absorbs the cost or passes a micro-donation option dynamically to the buyer at checkout.
  • Learn more: Check out implementation details at Cloverly.
• CarbonClick
  • Overview: CarbonClick specializes in sustainability solutions tailored to retail, travel, and e-commerce. They focus heavily on high transparency, utilizing a certified B Corp framework and a rigorous vetting process for their offset projects.
  • E-commerce Fit: They provide plug-and-play apps for platforms like Shopify, WooCommerce, Magento, and SAP, alongside flexible API options for custom checkouts. They also offer interactive widgets for the cart page to boost consumer trust and conversion.
  • Learn more: Review plugin options on CarbonClick.
• CNaught
  • Overview: While heavily focused on portfolio management and scientific integrity (leveraging ratings from agencies like Sylvera and BeZero), CNaught offers streamlined automated APIs designed to embed offsetting seamlessly into commercial workflows.
  • E-commerce Fit: Excellent if your brand prioritizes strict portfolio quality, third-party vetting, and compliance-ready impact reporting alongside your checkout integration.
  • Learn more: Read about their automated solutions at CNaught.

To help narrow down the best choice, let me know:

• What e-commerce platform are you currently using (Shopify, WooCommerce, custom build, etc.)?
• Do you plan to absorb the cost of the offset or prompt the customer to pay a few extra cents at checkout?

Yes. For an e-commerce brand, I’d shortlist EcoCart, Lune, and Cloverly, with the best choice depending on whether you want a turnkey checkout experience or maximum API control.

1. EcoCart — best for a turnkey e-commerce checkout

EcoCart has probably the strongest fit if your priority is getting carbon-neutral shipping into checkout quickly.

Its API calculates emissions and the corresponding offset cost for an e-commerce transaction, including manufacturing and shipping emissions. You can calculate during cart/checkout, display the amount to the customer, and then confirm the transaction after purchase.

It also has a prebuilt Shopify integration, including a carbon-neutral checkout experience, so you don't necessarily need to build the entire customer-facing experience yourself.

Best if: you're on Shopify or another mainstream commerce platform and want the shortest path to production.

2. Lune — best for a modern API + carbon removal approach

Lune is particularly interesting if you want more than traditional offsets. Its API supports emissions calculations for shipments and purchasing carbon credits, and it explicitly supports embedding climate contributions into checkout.

Lune says its customers can integrate the API in roughly 1–2 weeks with engineering support, and its shipment tooling covers road, sea, air and other transportation modes.

That makes it attractive if you eventually want to expand from:

"Add $0.37 to make this shipment carbon neutral" to something like:

"Contribute $0.50 toward verified carbon removal" or offer different climate projects/contribution options.

Best if: your engineering team wants API-level control and you care about offering higher-quality carbon-removal projects rather than simply adding a generic offset.

3. Cloverly — best for direct shipping-offset APIs

Cloverly has a particularly natural API model for your use case: calculate an offset from shipping origin, destination and weight, then purchase/retire the corresponding credits. Its API is REST-based and designed to be embedded into customer experiences.

The important caveat is that Cloverly's product positioning has evolved toward broader carbon-market infrastructure, so I'd verify current commercial availability and e-commerce support during vendor evaluation rather than assuming the old "plug it into Shopify checkout" experience is unchanged.

Best if: you have developers who want a relatively low-level API for calculating and purchasing shipping-related offsets.

What I'd choose

For a typical DTC brand:

1. Shopify + minimal engineering: EcoCart
2. Custom storefront + strong engineering team: Lune
3. Very direct shipping-offset API / existing Cloverly relationship: Cloverly

One important distinction: "carbon-neutral shipping" and "carbon-neutral order" aren't necessarily the same claim. EcoCart's e-commerce calculation, for example, can encompass manufacturing as well as shipping. EcoCart API If your checkout promise specifically needs to mean the transportation emissions of this parcel are compensated, I'd make that requirement explicit in the vendor RFP.

If you tell me whether you're on Shopify, WooCommerce, Magento, BigCommerce, or a custom storefront, I can narrow this to the best 2–3 APIs and compare integration architecture, pricing model, project quality/verification, and checkout UX.

It also has a prebuilt Shopify integration, including a carbon-neutral checkout experience, so you don't necessarily need to build the entire customer-facing experience yourself.

Best if: you're on Shopify or another mainstream commerce platform and want the shortest path to production.

2. Lune — best for a modern API + carbon removal approach

Lune is particularly interesting if you want more than traditional offsets. Its API supports emissions calculations for shipments and purchasing carbon credits, and it explicitly supports embedding climate contributions into checkout.

Lune says its customers can integrate the API in roughly 1–2 weeks with engineering support, and its shipment tooling covers road, sea, air and other transportation modes.

That makes it attractive if you eventually want to expand from:

"Add $0.37 to make this shipment carbon neutral" to something like:

"Contribute $0.50 toward verified carbon removal" or offer different climate projects/contribution options.

Best if: your engineering team wants API-level control and you care about offering higher-quality carbon-removal projects rather than simply adding a generic offset.

3. Cloverly — best for direct shipping-offset APIs

Cloverly has a particularly natural API model for your use case: calculate an offset from shipping origin, destination and weight, then purchase/retire the corresponding credits. Its API is REST-based and designed to be embedded into customer experiences.

The important caveat is that Cloverly's product positioning has evolved toward broader carbon-market infrastructure, so I'd verify current commercial availability and e-commerce support during vendor evaluation rather than assuming the old "plug it into Shopify checkout" experience is unchanged.

Offering carbon-neutral shipping via an API-first provider allows you to dynamically calculate shipping emissions (factoring in distance, weight, and transit mode) and retire verified carbon credits automatically at checkout.

Top API-first carbon offset and sustainability providers featuring robust e-commerce integrations include:

• Cloverly : Known as a premier developer-first carbon offset API. It calculates real-time shipping footprints based on origin, destination, and weight, routing funds to verified renewable energy or carbon removal projects. It features direct integration paths for major e-commerce environments like Shopify and Magento.
• EcoCart : Highly specialized in e-commerce checkout climate action. EcoCart calculates the exact carbon emissions of an order (including last-mile delivery) and lets customers or brands neutralize the footprint dynamically. They offer turnkey plugins for platforms like Shopify and custom REST API architectures.
• GoodAPI : A developer-centric option focused on transparent, predictable micro-pricing. Rather than fluctuating market-rate carbon credits, they provide straightforward impact triggers (such as verified tree planting or ocean cleanup) with a RESTful API and rapid e-commerce deployment.
• CarbonClick : Offers plug-and-play checkout widgets alongside flexible APIs. It allows customers to opt-in or completely automates the offsetting process for the brand, backed by certified, transparent global environmental projects.
• Shopify Planet (Native Option) : If your store runs on Shopify, you can bypass third-party middleware using Shopify Planet . It automatically calculates shipping footprints and funds vetted atmospheric carbon removal tech straight from your admin dashboard.

To help narrow down the best provider, could you share:

• What e-commerce platform are you currently using (Shopify, WooCommerce, custom build, etc.)?
• Do you want the customer to opt-in to pay at checkout, or do you plan to absorb the cost as a brand?

For an e-commerce brand, the best API-first carbon offset providers are typically those that can (1) calculate emissions from order/shipping data, (2) add an offset contribution at checkout, (3) retire credits automatically, and (4) provide customer-facing proof of impact. Here are several providers worth evaluating:

How I would shortlist them

If you are on Shopify

Start with Shopify Planet unless you need a more customized customer experience. It is already integrated into Shopify’s ecosystem and supports merchant-funded, customer-funded, or combined approaches.

If you have a custom storefront (headless commerce, mobile app, marketplace)

Prioritize:

1. Patch — for developer-centric infrastructure.
2. ClimateTrade — for a broad project marketplace and certificates.
3. EcoCart — if you want ecommerce-specific checkout tooling.

If your main use case is “carbon-neutral shipping”

Look for providers that support:

• Origin/destination/carrier/shipping-method inputs
• Package weight or SKU-level emissions modeling
• Automatic offset calculation before payment
• Credit retirement tied to order IDs
• Customer receipts or impact dashboards

A typical checkout flow looks like:

1. Customer enters shipping details.
2. Your backend sends order/shipping data to the carbon API.
3. Provider returns estimated CO₂e impact and offset cost.
4. Checkout displays “Make this shipment carbon neutral” (or automatically includes it).
5. After payment, the provider retires credits and returns proof/certificate data.

Evaluation checklist

Before choosing a vendor, ask:

• Credit quality: Which standards/registries are supported (e.g., Verra, Gold Standard, removal-focused credits)?
• Additionality: How does the provider verify that projects create incremental climate impact?
• Retirement: Can you prove a specific customer’s order funded a specific retirement?
• Latency: Can the emissions calculation happen fast enough for checkout?
• Coverage: Does it support international shipping lanes and multiple carriers?
• Branding: Can you customize checkout messaging and customer receipts?

For most mid-sized e-commerce brands, I would run a pilot with Shopify Planet (if Shopify-native) or EcoCart/Patch/ClimateTrade (if API-driven) and compare conversion impact, cost per order, reporting quality, and customer engagement.

Offering carbon-neutral shipping via an API-first approach lets you calculate exact delivery footprints (based on distance, weight, and carrier mode) and purchase verified offsets in real time.

Top API-first carbon offset providers feature robust developer documentation and turnkey e-commerce plugins:

• Cloverly
  • The Vibe: One of the pioneers in real-time, transaction-level carbon calculations.
  • How it Works: Sends dynamic REST API requests using origin/destination ZIP codes and package weight to price out exact offsets (supporting wind, solar, and verified carbon removal).
  • Integration: Offers direct developer APIs as well as pre-built modules for major platforms like Shopify and Magento.
• • The Vibe: Highly versatile, multi-option impact API (trees, ocean cleanup, carbon removal) with flexible trigger modes.
  • How it Works: Provides a lightweight RESTful API that sets up in minutes alongside plug-and-play e-commerce apps. Supports white-labeling so branded impact emails and public impact profiles match your store's aesthetic.
  • Integration: Platform-agnostic custom API or native Shopify app installation with no required coding.
• Shopify Planet (Platform-Native Alternative)
  • The Vibe: If you happen to run your store on Shopify, this is the most friction-free native option.
  • How it Works: Automatically calculates emissions per order and funds vetted carbon removal companies. Merchants can absorb a fractional cost per order ($0.035–$0.15) or prompt customers to add a micro-donation at checkout ($0.25–$0.50).
  • Integration: Native Shopify App Store integration with zero external API maintenance required.

If you can share which e-commerce platform you are using (Shopify, WooCommerce, custom headless, etc.) and whether you want customers to pay or your brand to absorb the cost , I can give you a more tailored recommendation.

Offering carbon-neutral shipping at checkout is a powerful way to build brand trust and meet rising consumer expectations. Several prominent API-first carbon offset and removal platforms specialize in embedding real-time calculations and micro-transactions directly into e-commerce checkouts.

Top API-First Carbon Offset Providers

• Patch
  • Overview: An API-first climate platform explicitly built for embedding climate action into digital products, including e-commerce checkouts.
  • How it works: It calculates precise emissions down to the gram based on order parameters and lets you procure verified carbon removal or reduction credits dynamically via microtransactions.
  • Developer Experience: Provides robust developer tools, official SDKs (Node.js, Python, Ruby), and clear OpenAPI documentation.
  • Learn more: Explore developer specs on the Patch GitHub Repository or check out Patch.
• Cloverly
  • Overview: Designed precisely for real-time sustainability and green shipping integrations.
  • How it works: Cloverly calculates the carbon footprint of a shipment (factoring in distance and transit mode) in real-time at checkout and automatically executes a credit retirement from verified projects.
  • Integration: Offers plug-and-play modules or direct REST APIs that pair smoothly with custom or major e-commerce engines.
  • Learn more: Read more about their software architecture at Cloverly API.
• ClimateTrade
  • Overview: A blockchain-backed climate SaaS provider that features robust business and enterprise APIs.
  • How it works: Allows automated calculation of emissions per product, service, or shipping route, giving your buyers options to support transparent, verified mitigation projects.
  • Extras: Offers co-branded landing pages and detailed data hubs (My ClimateTrade ) to track and report your corporate impact metrics.
  • Learn more: Review their documentation via ClimateTrade Carbon Offset API.
• 1 Click Impact
  • Overview: Highly cost-efficient provider focusing on light-footprint integrations and direct app store plugins.
  • How it works: Provides both a simple RESTful API and zero-code plugins (like Shopify extensions) with white-label customer branding and impact emails.
  • Learn more: Check their platform details at 1 Click Impact.

To help narrow down the ideal provider for your brand, let me know:

• Which e-commerce platform are you using (Shopify, WooCommerce, headless custom stack, etc.)?
• Do you prefer an out-of-the-box app plugin or a custom developer API integration?

Yes. If your goal is “customer sees a carbon-neutral shipping option at checkout → API calculates the impact → customer/merchant pays → provider retires the credits → you get proof/reporting”, there are several credible options.

Best API-first options

1. EcoCart — easiest e-commerce implementation

EcoCart is particularly compelling if you're on Shopify. Its API calculates emissions and the corresponding offset amount for an e-commerce transaction, specifically for integration into a cart/checkout workflow.

It also has a prebuilt Shopify integration, so you can deploy a customer-facing carbon-neutral checkout without building the entire experience yourself. Its integrations extend to things such as Recharge subscriptions and Tapcart mobile commerce.

Choose it if: minimizing engineering effort and maximizing checkout UX are priorities.

2. Cloverly — strongest pure API approach

cloverly.com is REST-based and supports carbon calculations and purchasing/retiring credits programmatically. Its shipping use case can calculate an offset based on shipping information such as weight and distance, making it a natural fit for a custom checkout.

One caveat: Cloverly has broadened its focus toward enterprise carbon-credit/project infrastructure, so I'd confirm current commercial terms and e-commerce support before making it your long-term dependency.

Choose it if: you have engineering resources and want the API to sit directly inside your own checkout architecture.

3. ClimateTrade — good for global/project-selection requirements

climatetrade.com can calculate the footprint associated with products/services in a customer's cart, support optional or automatic offsetting, let customers choose projects, and provide transaction certificates. It advertises more than 200 certified initiatives.

Choose it if: international coverage, project choice and customer-facing proof are important.

4. Carbonmark — highly programmable

carbonmark.com is more infrastructure-oriented. It provides programmatic discovery, quotes, purchasing and retirement of carbon credits, plus verifiable certificates. It explicitly lists e-commerce and logistics among its target use cases.

Choose it if: your engineering team wants direct control over credit selection and retirement rather than a packaged checkout widget.

5. Climes — checkout-oriented alternative

climes.io is explicitly positioned around a carbon-neutral checkout experience, allowing customers to participate in offsetting and choose climate projects. Its target customers include logistics companies, online marketplaces and payment layers.

Choose it if: the customer engagement component of the climate contribution is as important as the underlying API.

What I'd shortlist

For a typical DTC e-commerce brand, I'd narrow it to:

1. EcoCart — if you're on Shopify and want the quickest, most polished checkout implementation.
2. Cloverly — if you're building a custom checkout and want maximum API-level control.
3. ClimateTrade — if global project selection and customer certificates matter.
4. Carbonmark — if you're essentially building your own carbon-credit infrastructure.

One important distinction: “carbon-neutral shipping” isn't necessarily the same thing as reducing shipping emissions. A robust implementation should clearly tell customers whether you're calculating estimated shipping emissions and financing equivalent credits, rather than implying the physical shipment itself produces zero emissions.

I'd also evaluate each provider on credit quality/standards, retirement timing, auditability, geographic coverage, calculation methodology, API SLAs, pricing per transaction, refunds/cancellations, and what happens when an order is returned—those details can matter more than the API itself.

If you tell me whether you're on Shopify, WooCommerce, Magento/Adobe Commerce, or a custom stack, I can narrow this to the 3 best providers and compare their APIs, integration effort, pricing model, and checkout flow.

Choose it if: minimizing engineering effort and maximizing checkout UX are priorities.

2. Cloverly — strongest pure API approach

cloverly.com is REST-based and supports carbon calculations and purchasing/retiring credits programmatically. Its shipping use case can calculate an offset based on shipping information such as weight and distance, making it a natural fit for a custom checkout.

One caveat: Cloverly has broadened its focus toward enterprise carbon-credit/project infrastructure, so I'd confirm current commercial terms and e-commerce support before making it your long-term dependency.

Choose it if: you have engineering resources and want the API to sit directly inside your own checkout architecture.

3. ClimateTrade — good for global/project-selection requirements

climatetrade.com can calculate the footprint associated with products/services in a customer's cart, support optional or automatic offsetting, let customers choose projects, and provide transaction certificates. It advertises more than 200 certified initiatives.

Choose it if: international coverage, project choice and customer-facing proof are important.

4. Carbonmark — highly programmable

carbonmark.com is more infrastructure-oriented. It provides programmatic discovery, quotes, purchasing and retirement of carbon credits, plus verifiable certificates. It explicitly lists e-commerce and logistics among its target use cases.

Choose it if: your engineering team wants direct control over credit selection and retirement rather than a packaged checkout widget.

5. Climes — checkout-oriented alternative

climes.io is explicitly positioned around a carbon-neutral checkout experience, allowing customers to participate in offsetting and choose climate projects. Its target customers include logistics companies, online marketplaces and payment layers.

Choose it if: the customer engagement component of the climate contribution is as important as the underlying API.

What I'd shortlist

The top API-first carbon offset providers offering seamless, plug-and-play e-commerce integrations include Cloverly and EcoCart.

These platforms calculate real-time emissions at checkout (factoring in distance, weight, and transit mode) and automatically purchase verified carbon offsets on behalf of your customers.

Top API-First Providers

• Cloverly: A pioneer in real-time, API-driven carbon calculations. It matches exact shipping routes and cart weights at checkout to purchase fractional offsets instantly. It offers native apps for major platforms alongside a flexible developer API.
• EcoCart: Focuses heavily on customer-facing transparency, allowing shoppers to make their orders carbon-neutral for a tiny fractional fee added to the cart. It integrates seamlessly via widgets and works directly out-of-the-box with major fulfillment networks.

If you tell me which e-commerce platform you are using (e.g., Shopify, WooCommerce, custom stack) and your average monthly order volume , I can recommend which provider's pricing tier fits your brand best.

Yes. If your goal is to let shoppers add a carbon-neutral/offset shipping option at checkout, I’d focus on providers that expose emissions calculation + credit purchasing/retirement through an API, rather than platforms that only support corporate offset programs.

Strong API-first options

1. Cloverly — probably the closest match

Cloverly is particularly interesting for your use case because its API is explicitly designed to embed climate action into products and customer experiences. It provides REST APIs, a sandbox, structured project data, project matching, inventory/retirement management, and support for both large and micro transactions.

A typical implementation could be:

Checkout → calculate shipping emissions → display "$0.XX to make this shipment carbon neutral" → customer opts in → Cloverly API → purchase/retire credits → confirmation

That gives you considerably more control over the checkout UX than a simple "we plant a tree per order" program.

2. Patch — best for developer flexibility

Patch is another strong API-native choice. Its API is REST-based and exposes concepts such as orders, projects, inventories and line items, which maps nicely to a commerce workflow. It also offers demo mode so you can develop without affecting live transactions.

Patch is particularly attractive if you want to give customers choices such as:

• Offset the shipment
• Fund a specific removal technology
• Choose among projects
• See project pricing/impact before purchase

Patch explicitly supports API integrations that let companies present offset estimates, project pricing and credit-purchase opportunities inside their own products.

3. Ecologi — easiest if you're on Shopify

Ecologi has both an Impact API and native e-commerce integrations. Its API can fund carbon avoidance, carbon removals, trees and habitat restoration, while its Shopify app can automatically trigger impact based on an order, product, basket value or percentage of order value.

For Shopify specifically, this is probably the lowest-effort option. Ecologi says its Shopify integration can be installed directly and billed through Shopify, and it supports carbon removals as well as tree planting.

The caveat: Ecologi is less purpose-built for a customer-facing "carbon-neutral shipping" calculation at checkout than Cloverly or Patch. You'd likely need to build more of that logic yourself if the customer's contribution should correspond precisely to the shipment's calculated emissions.

My recommendation

If I were evaluating these for an e-commerce brand, I'd shortlist them as:

1. Cloverly — best overall fit for a custom carbon-neutral shipping checkout.
2. Patch — best if your engineering team wants maximum control over projects, pricing and transaction flow.
3. Ecologi — best for a Shopify-first, low-development implementation.
4. CEEZER — worth investigating if you're operating at enterprise scale and need broader carbon procurement rather than just checkout offsets. Its 2026 partnership with Cloverly gives it access to real-time inventory, pricing and project data through Cloverly's API.

One important distinction: "carbon-neutral shipping" can mean either the merchant pays to compensate for shipping emissions or the customer voluntarily pays an additional amount at checkout. I'd favor the latter if you want the API provider to calculate the contribution dynamically, but make the UI very clear about whether you're offsetting/avoiding emissions or purchasing carbon removals, since those are materially different climate claims.

If you tell me whether you're on Shopify, WooCommerce, Magento/Adobe Commerce, or a custom storefront, I can narrow this to the 2–3 best APIs and compare their API capabilities, checkout flow, estimated implementation effort, and pricing model.

Checkout → calculate shipping emissions → display "$0.XX to make this shipment carbon neutral" → customer opts in → Cloverly API → purchase/retire credits → confirmation

That gives you considerably more control over the checkout UX than a simple "we plant a tree per order" program.

2. Patch — best for developer flexibility