Agent payments glossary
The terms that come up when you let an AI agent pay, defined plainly and linked to their official specs.
Terms
- MCP serverAn MCP server is a service that offers tools, resources or prompts to AI applications using the Model Context Protocol, an open protocol built on JSON-RPC 2.0.
- Payment intentA payment intent is an object representing a payment that has been requested but not necessarily completed, which moves through defined states such as awaiting approval, submitted, confirmed or cancelled.
- Idempotency keyAn idempotency key is a unique value a client attaches to a request so that, if the same request is sent again with the same key, the server returns the original result instead of performing the action a second time.
- Token allowance (ERC-20 approve)A token allowance is the amount of an ERC-20 token that an owner has authorised a specific spender address to transfer from the owner's account, set with approve and spent with transferFrom.
- Auto-approve limitAn auto-approve limit is the largest single payment an agent may make without a person approving it, within any other caps that apply.
- HTTP 402 Payment Required402 Payment Required is an HTTP response status code that RFC 9110 lists as 'reserved for future use', meaning HTTP itself defines no standard behaviour for it.
- x402 facilitatorAn x402 facilitator is a service that verifies x402 payment payloads and settles them on-chain on behalf of a resource server, through /verify and /settle endpoints.
- Stablecoin (USDC)A stablecoin is a blockchain token designed to keep a stable value relative to a reference asset, usually a currency such as the US dollar; USDC is a dollar stablecoin issued by Circle.
- Shared Payment Token (SPT)A Shared Payment Token (SPT) is a Stripe credential that grants an agent or seller scoped use of a customer's payment method, such as a card, with usage and expiration limits.
For step-by-step answers, see the guides.
Try it with Veyra
Veyra gives an AI agent one MCP endpoint with per-payment, daily, auto-approve and ask limits and an optional recipient allowlist, all enforced server-side. Start free on a simulated wallet that moves no money, then connect your own wallet for USDC on Base.
This page explains how agent payments and the related technology work. It is not financial, investment, legal or tax advice. Protocols and provider features change; check the linked official sources before relying on a detail.