Machine payments HTTP 402

For APIs and paid digital resources, agents can pay per request without a checkout page: the server answers HTTP 402 with payment requirements, the agent retries with a payment credential and receives the resource plus a receipt. Stripe supports two such protocols: MPP (Machine Payments Protocol, co-authored by Stripe and Tempo), which accepts cards through Shared Payment Tokens from 0.50 USD and stablecoins from 0.01 USDC, and x402, where stablecoin payments on Base settle through Coinbase's facilitator and the 402 response carries a payment-required header. Stripe asks integrations submitted to its Stripe Directory, a catalogue that helps agents find businesses, for a link to their llms.txt file and example prompts.