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How to pay for a call

Every paid route speaks x402 v2. You need an x402 client and a Base wallet holding a little USDC. There is no account to create.

The flow

1. Send the request with no payment. The tool answers 402 and a PAYMENT-REQUIRED header (base64 JSON). It lists scheme: "exact", network: "eip155:8453" (Base mainnet), asset = USDC 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913, amount in USDC base units (6 decimals) and payTo = 0xfbF7413bcB3a604936775C96FDbe0b0C9c9E37F5.
2. Your client signs an EIP-3009 USDC transfer authorization for exactly that amount and resends the same request with a PAYMENT-SIGNATURE header.
3. The tool asks the facilitator (PayAI) to verify, builds the answer, and settles only if the answer is a success. The PAYMENT-RESPONSE header carries the settlement receipt.

When you are not charged

• Any response with status 400 or higher: bad input, not found, upstream failure or an internal error. Settlement is cancelled.
• If settlement itself fails, you get the error and no data, and nothing moves.
• A replayed payment header cannot settle twice (each authorization has a one-time nonce).

Discovery

• /.well-known/x402: every live paid resource with its absolute URL and accepted payment.
• catalog.json: every tool with status, prices, routes and links.
• llms.txt and llms-full.txt: the same, written for language models.
• Each tool also serves its own /openapi.json and /.well-known/x402.