---
id: guides/pay-per-call-with-x402
title: "Pay per call with x402"
description: "Pay for a Nova tool call inline, in STX, sBTC or USDCx on Stacks."
product: nova
canonical: https://zeroauthoritydao.ai/docs/guides/pay-per-call-with-x402
related: [guides]
tokens: 191
---

# Pay per call with x402

Your code will pay for a paid Nova tool in the same request, and only be charged if the tool runs.

## Call the tool
Send a POST to the tool's `/api/tools/<slug>/run` endpoint with its input. A paid tool answers with HTTP 402 and a `payment-required` header listing the accepted payments. [Full guide](https://zeroauthoritydao.ai/docs/build/x402.md)

## Pick a token and sign
Choose STX, sBTC or USDCx from the options. Build a sponsored Stacks transaction with zero fee, so the payer pays no gas, and sign it. [Full guide](https://zeroauthoritydao.ai/docs/build/x402.md)

## Retry with the payment
Send the same request again with a `payment-signature` header holding the signed payment. [Full guide](https://zeroauthoritydao.ai/docs/build/x402.md)

## Read the result
You get the tool output and a receipt in the `payment-response` header. Payment settles only after the tool succeeds, so a failed call costs nothing. [Full guide](https://zeroauthoritydao.ai/docs/build/x402.md)