> ## Documentation Index > Fetch the complete documentation index at: https://docs.particle.pro/llms.txt > Use this file to discover all available pages before exploring further. # payment_required > The request had no credential and the endpoint is billable — pay per request with x402 or authenticate with an API key | | | | ------------------ | ---------------------- | | **HTTP status** | `402 Payment Required` | | **Error code** | `payment_required` | | **Resolve action** | `pay_per_request` | ## What happened The request carried no credential and the endpoint is billable. Particle Pro accepts an [x402](/x402) micropayment in place of a credential, so instead of a `401` the response is a `402` whose `PAYMENT-REQUIRED` header holds the machine-readable payment requirements (network, asset, amount, recipient). The body's `detail` states the price in dollars. The same code is returned, with a `PAYMENT-RESPONSE` header, when a payment was accepted but could not be settled on-chain after the request ran. The response was withheld. A payment the facilitator rejected transferred nothing; if the failure was a timeout the transfer may still have gone through, so retry the identical request with the same `PAYMENT-SIGNATURE` first (an authorization executes at most once) and sign a new payment only after an explicit rejection. ## How to fix Decode the `PAYMENT-REQUIRED` header (base64 JSON), sign an EIP-3009 USDC transfer for `accepts[0].amount` to `accepts[0].payTo` on `accepts[0].network`, and repeat the identical request with the payment payload in the `PAYMENT-SIGNATURE` header. Any x402 v2 client library does this automatically. If your operator has a Particle Pro account, ask for a `pp_…` key and send it as `X-API-Key`. Sending any credential — even an invalid one — disables the payment path for that request and returns the normal `401` on failure.