acp-payment-handlers

name	acp-payment-handlers
description	Implement ACP payment handlers — pluggable payment method specifications including tokenized cards, seller-backed methods (gift cards, points, store credit), and handler negotiation. Use when adding payment methods or building custom payment handler support.
allowed-tools	Read, Write, Edit, Bash, Grep, Glob, WebSearch, WebFetch

ACP Payment Handlers

Before writing code

Fetch live docs:

1. Web-search site:github.com agentic-commerce-protocol rfcs payment_handlers for the payment handlers RFC
2. Web-search site:github.com agentic-commerce-protocol rfcs seller_backed for seller-backed payment handler RFC
3. Fetch https://developers.openai.com/commerce/specs/payment/ for payment data structures
4. Web-search site:docs.stripe.com agentic-commerce payment handler for Stripe's handler implementation

Conceptual Architecture

What Payment Handlers Are

Payment handlers are pluggable specifications that define how a particular payment method works within ACP. Each PSP or merchant publishes handler specs, and agents/merchants negotiate which handlers they mutually support.

This inverts the traditional integration model — instead of hardcoding payment methods into the protocol, handlers are discoverable and composable.

Handler Identification

Each handler has a reverse-DNS name and version:

• dev.acp.tokenized.card — Tokenized credit/debit cards (Stripe SPT)
• dev.acp.seller_backed.saved_card — Pre-stored cards on merchant
• dev.acp.seller_backed.gift_card — Gift cards with number/PIN
• dev.acp.seller_backed.points — Loyalty/rewards points
• dev.acp.seller_backed.store_credit — Account balance/store credit

Handler Structure

Each payment handler spec defines:

• id — Unique instance identifier within the session
• name — Specification name in reverse-DNS format (e.g., dev.acp.tokenized.card)
• version — Spec version
• spec — URL to the handler specification
• requires_delegate_payment — Whether the agent must call /delegate_payment (true for tokenized cards)
• requires_pci_compliance — Whether PCI DSS scope is affected
• psp — Which PSP processes this handler
• config_schema — JSON Schema for merchant configuration
• instrument_schemas — JSON Schema(s) for the payment instrument data the agent sends

Tokenized Card Handler

The primary handler — uses Stripe's delegated payment:

1. Agent provisions SPT via Stripe
2. Agent sends SPT as the instrument credential in complete
3. Merchant charges via Stripe using the SPT
4. requires_delegate_payment: true

Seller-Backed Handlers

These bypass the PSP — the merchant directly manages the payment:

• Saved card — Customer has a card on file with the merchant
• Gift card — Number + optional PIN
• Points — Loyalty program balance
• Store credit — Account balance
• requires_delegate_payment: false
• requires_pci_compliance: false (except saved cards)

Handler Negotiation

During capability negotiation:

1. Agent advertises supported payment handlers in capabilities.payment.handlers[]
2. Merchant responds with handlers they accept
3. Intersection determines available payment methods for the session
4. Agent picks one and provides the appropriate instrument data

Payment Data Structure

When completing a checkout, the agent provides:

• handler_id — Which handler is being used
• instrument — type + credential (shape defined by handler's instrument schema)
• Optional billing_address

Best Practices

• Support multiple handlers to maximize conversion
• Advertise all accepted handlers in capability negotiation
• Validate instrument data against the handler's instrument schema
• Handle handler-specific errors (e.g., insufficient points, expired gift card)
• Log handler usage for payment method analytics

Fetch the payment handlers RFC and instrument schemas from the GitHub repo for exact field definitions before implementing.