PipRail
both speak HTTP 402
Two ways to pay an agent

MPP vs. x402

Same handshake. The fork is custody — who holds the money once the agent agrees to pay.
MPPStripe + Tempo
A custodian holds it.
held by Stripe · ~1.5% fee
permissioned chain · can freeze
x402self-custody
Nobody holds it.
wallet-to-wallet · 0% fee
any of ~29 chains · you verify