> For the complete documentation index, see [llms.txt](https://docs.vapinetwork.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.vapinetwork.ai/protocol/x402-payments.md).

# x402 payments

vAPI Call uses x402 for pay-per-call APIs. Payments use USDC on Base and are authorized from a buyer-controlled wallet for one request at a time.

## Payment flow

1. **Request.** The buyer sends the API request without a payment header.
2. **402 challenge.** The API returns `402 Payment Required` with an x402 exact challenge. The challenge states the network, USDC asset, recipient, amount, and validity window.
3. **Signed payment.** The buyer client validates those fields and the user's per-call maximum. The buyer-local wallet also checks its local daily limit. The buyer approves the network and signs a narrowly scoped EIP-3009 authorization.
4. **Settlement.** The client retries the same request once with the authorization. The provider or its facilitator settles the payment.
5. **Response.** The provider returns the API response and settlement result.

The signature fixes the recipient, value, token domain, chain, nonce, and time window. Discovery cannot change those fields after the buyer signs.

<figure><img src="/files/scoSYiVqboODiE7p6Dr1" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
The provider's live 402 challenge is the payment source of truth. A price or recipient stored in discovery can become stale. Validate the live challenge before signing.
{% endhint %}

Fees per listing source are on [Fees and the splitter](/for-vendors/fees-and-splitter.md).


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