How can merchants verify AI agent identity during checkout?

Merchant Verification Checklist (At Checkout)

To accept an agent payment, verify:

• Receipt signature — consent receipt is signed by a trusted issuer key.
• Scope match — the checkout action is in consent_scope.
• Constraint match — amount, currency, merchant/category, and time window match receipt limits.
• Replay protection — receipt nonce has not been used before (per merchant/instance).
• Expiry — receipt validity window has not elapsed (including offline freshness policy).
• Evidence output — return a binary decision with proof/audit record for disputes.

See also: merchant verification and consent framework.

Merchant Verification Graph

This diagram shows the merchant-side verification pipeline before accepting a payment:

Merchant Failure Modes (At Checkout)

Merchants can integrate via AffixIO Merchant SDK or via API calls to a verification endpoint.

What Merchants Need to Verify

Merchants check three things:

1. Receipt signature — Is the consent receipt signed by a trusted issuer?
2. Scope and constraints — Does the receipt allow this action, at this amount, for this merchant?
3. Replay status — Has this receipt been used before?

Merchant Verification Flow

Signature Verification

The merchant verifies the Ed25519 signature on the consent receipt using the issuer's public key. This confirms the receipt was not tampered with and was issued by a trusted authority. See authentication mechanisms.

Scope and Constraint Checks

The merchant confirms: the requested action (e.g., "pay") is in the receipt's consent_scope, the transaction amount is within max_amount, the currency matches, and the merchant ID matches. If the receipt specifies allowed_categories, the merchant's category must be included.

Replay Protection

The merchant checks the receipt nonce against its nonce store. If the nonce has been seen before, the transaction is rejected. For multi-location merchants, a shared nonce store (Redis, database) is recommended.

Integration Points

Merchant integration options:

• API call — Send receipt + transaction context to AffixIO verification endpoint
• SDK — Use the AffixIO Merchant SDK for local verification
• Webhook — Receive verification results asynchronously

What Merchants Should Log

For each agent transaction, log: receipt ID, agent ID, verification result, amount, timestamp. This creates an audit trail for disputes and chargebacks. The proof of permission object serves as evidence.