> For the complete documentation index, see [llms.txt](https://docs.rigoblock.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rigoblock.com/x402-v2-payment-flow.md). # x402 v2 Payment Flow 1. Make a request → server responds `402 Payment Required` and may include a `PAYMENT-REQUIRED` header describing accepted payment requirements 2. Create the payment payload for USDC on Base (chain 8453), typically with `@x402/core` 3. Retry with the `X-Payment` header → receive structured data; successful 2xx responses may include a `PAYMENT-RESPONSE` settlement receipt **Use the** [**@x402/core**](https://www.npmjs.com/package/@x402/core) **SDK** — it handles payment flow automatically. **Payment:** USDC on Base (eip155:8453) — CDP facilitator at api.cdp.coinbase.com **Integration guide & agent-to-agent architecture:** **Supported chains:** Ethereum (1), Base (8453), Arbitrum (42161), Optimism (10), Polygon (137), BNB (56), Unichain (130) --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.rigoblock.com/x402-v2-payment-flow.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.