PROTOCOL COMPARISON

Machine Payments Protocol (MPP) vs. x402

MPP and x402 both use HTTP 402 for machine payments, but they differ in payment-method scope and integration semantics. Neither replaces delegated purchase authority.

Published by MandateShield · Updated July 24, 2026

SHORT ANSWER

Which protocol should an AI-agent payment flow use?

Use the protocol supported by the service and payment rail. MPP is a payment-method-agnostic HTTP authorization framework; x402 is designed for HTTP-native onchain payments. In either case, separately verify that the final provider, resource, amount and currency remain inside signed human or enterprise authority.

DimensionMPPx402
Primary purposeNegotiate and authorize machine payments over HTTPPay for HTTP resources with onchain assets
Payment-method scopePayment-method agnostic, with method-specific challenges and credentialsOnchain payment requirements selected from a 402 response
Common transport signalHTTP 402 with protocol authorization fieldsHTTP 402 with payment requirements and a signed payment payload
Delegated authorityNot automatically proof that a human approved the exact purchaseNot automatically proof that a human approved the exact purchase
MandateShield supportNormalize final terms into a signed CUSTOM envelope; raw MPP is not parsed todayNormalize the selected x402 requirement into the strict verification projection
Payment executionPerformed by the selected MPP payment method, not MandateShieldPerformed by the x402 client or facilitator, not MandateShield

MPP

Use this side when

  • A paid API or agent service needs a payment-method-neutral HTTP contract.
  • The service may accept cards, stablecoins, Lightning or another method.
  • Your ecosystem already exposes an MPP challenge and credential flow.

x402

Use this side when

  • The resource is sold through an x402-compatible onchain flow.
  • The client can satisfy the network and asset requirements exactly.
  • A facilitator or direct onchain verification is part of the architecture.

PRACTICAL ARCHITECTURE

How they work together

They are alternative payment-protocol layers, not authorization policies. Before constructing either payment credential, a trusted integrator can normalize the final purchase into MandateShield, reserve the delegated budget and require one audience-bound consumption at the gateway.

Official MPP specification →Official x402 documentation →Protocol support evidence →