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xWell supports two HTTP 402 payment protocols. Your agent doesn’t need to know the difference — xWell auto-detects and handles both.

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x402

An open payment standard that uses the HTTP 402 status code for programmatic payments.

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Flow

  1. Agent requests a resource — service returns 402 Payment Required
  2. Response includes payment details (amount, token, chain, recipient)
  3. xWell signs the payment in a secure enclave
  4. xWell retries the request with the payment credential
  5. Service verifies payment and returns the resource

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Supported chains

Base, Ethereum, Arbitrum, Optimism.

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MPP (Machine Payment Protocol)

An open standard for machine-to-machine payments via HTTP 402, co-developed by Tempo and Stripe.

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Flow

  1. Agent requests a resource — service returns 402 with a WWW-Authenticate: MPP challenge
  2. Challenge contains payment parameters
  3. xWell signs a credential in a secure enclave
  4. xWell retries with Authorization: MPP <credential> header
  5. Service verifies and returns a Payment-Receipt header

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Supported chains

Tempo, Solana.

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Protocol comparison

x402MPP
Auth mechanismPayment credential in headerHTTP challenge–credential–receipt
EVM chainsBase, Ethereum, Arbitrum, Optimism—
TempoNoYes
SolanaNoYes

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What happens when both are available

If a service supports both protocols, xWell prefers the chain where your wallet has the highest balance.