> ## Documentation Index > Fetch the complete documentation index at: https://docs.httpayer.com/llms.txt > Use this file to discover all available pages before exploring further. # Execute cross-chain relay payment > HTTPayer relay service for x402 cross-chain payments. **Flow:** 1. **First call (no X-Payment header)**: Returns 402 with payment instructions 2. **Second call (with X-Payment header)**: Executes relay payment flow **Supports:** - Cross-chain payments (EVM ↔ Solana) - Same-chain payments (EVM → EVM, Solana → Solana) - Automatic network selection based on target API (mainnet/testnet) **Fee Structure:** - HTTPayer charges a flat 3% relay fee on top of the target API's requested payment amount. - Example: For a \$0.10 target payment, fee = \$0.003, total = \$0.103 - Daily limits: \$100 per wallet, \$1000 system-wide ## OpenAPI ````yaml post /relay openapi: 3.0.0 info: title: HTTPayer Proxy API version: 1.0.0 description: >- HTTPayer is a payment router for 402 response codes and the x402 Protocol. Users can access APIs that use the x402 standard through the HTTPayer proxy. contact: name: HTTPayer Team url: https://httpayer.com servers: - url: https://api.httpayer.com description: Production server security: [] tags: - name: Relay description: Cross-chain payment relay endpoints - name: Account description: Account balance and limits endpoints - name: Webhooks description: Async task status and webhooks - name: LLM description: OpenAI-powered endpoints for translation and chat - name: Health description: Health check endpoints paths: /relay: post: tags: - Relay summary: Execute cross-chain relay payment description: > HTTPayer relay service for x402 cross-chain payments. **Flow:** 1. **First call (no X-Payment header)**: Returns 402 with payment instructions 2. **Second call (with X-Payment header)**: Executes relay payment flow **Supports:** - Cross-chain payments (EVM ↔ Solana) - Same-chain payments (EVM → EVM, Solana → Solana) - Automatic network selection based on target API (mainnet/testnet) **Fee Structure:** - HTTPayer charges a flat 3% relay fee on top of the target API's requested payment amount. - Example: For a \$0.10 target payment, fee = \$0.003, total = \$0.103 - Daily limits: \$100 per wallet, \$1000 system-wide parameters: - in: header name: X-PAYMENT schema: type: string description: >- x402 payment header (include on second call after getting payment instructions) required: false - in: header name: X-TIMEOUT schema: type: number description: Client timeout in milliseconds required: false - in: query name: format schema: type: string enum: - json - text default: text description: >- Response mode. When set to "json", wraps the proxied response as JSON; otherwise returns the raw proxied response as text. requestBody: required: false content: application/json: schema: $ref: '#/components/schemas/RelayRequest' responses: '200': description: > Relay payment successful. Response headers (included only when applicable): - X-Client-Payment: Transaction hash of the user's payment to HTTPayer after settlement (e.g., 0x123...) - X-HTTPayer-Webhook: Webhook ID to track async operation status (payment verification or refund) - X-Payment-Response: Details of HTTPayer's payment to the target API (v1, base64-encoded JSON) content: application/json: schema: type: object description: Response from target API text/plain: schema: type: string '400': description: Bad request content: application/json: schema: $ref: '#/components/schemas/Error' '402': description: X-PAYMENT header is required - Returns x402 payment instructions content: application/json: schema: type: object properties: x402Version: type: number example: 1 accepts: type: array items: $ref: '#/components/schemas/PaymentRequirements' '429': description: >- Too Many Requests - Daily spending limit exceeded OR server at capacity headers: Retry-After: description: Seconds to wait before retrying (only for rate limiting) schema: type: integer example: 5 content: application/json: schema: oneOf: - type: object description: Rate limiting response (server at capacity) properties: error: type: string example: Too Many Requests message: type: string example: >- Server is currently processing the maximum number of concurrent requests. Please try again in a moment. details: type: string example: 'Active requests: 50/50' retryAfter: type: integer example: 5 - type: object description: Daily spending limit response properties: error: type: string example: Daily wallet spending limit exceeded details: type: string currentSpend: type: number limit: type: number requestedAmount: type: number '500': description: Internal server error content: application/json: schema: $ref: '#/components/schemas/Error' '502': description: >- Bad gateway — target API returned an error or refused payment after retries content: application/json: schema: type: object properties: error: type: string example: Bad Gateway message: type: string example: Upstream API refused payment after 3 attempts webhook_id: type: string description: >- Present when background blockchain polling is active. Use GET /webhooks/:id to track settlement. example: 550e8400-e29b-41d4-a716-446655440000 components: schemas: RelayRequest: type: object properties: api_url: type: string description: The target API URL to call via the relay example: https://demo.httpayer.com/base-weather method: type: string enum: - GET - POST - PUT - DELETE - PATCH description: HTTP method for the target API example: GET json: type: object description: >- JSON body — serialized with Content-Type: application/json. Mirrors Python requests(json=...). data: description: >- Form-encoded body (object) or raw string body (string). Mirrors Python requests(data=...). oneOf: - type: object - type: string body: type: string description: >- Pre-serialized body string passed through unchanged — Content-Type is NOT set automatically. If you pass an object it will be JSON-stringified, but you must set Content-Type: application/json via headers yourself. Use json instead for automatic Content-Type handling. payload: type: object description: Deprecated alias for json. Use json instead. params: type: object description: Query parameters appended to the target URL headers: type: object description: Custom headers forwarded to the target API example: X-API-KEY: your-target-api-key Authorization: Bearer token123 auth: type: object description: >- Basic auth shorthand — converted to Authorization: Basic . Mirrors Python requests(auth=(...)). properties: username: type: string password: type: string cookies: type: object description: >- Cookie shorthand — merged into the Cookie header. Mirrors Python requests(cookies={...}). example: session: abc123 network: type: string enum: - base - base-sepolia - skale-base - skale-base-sepolia - solana - solana-mainnet-beta - solana-devnet description: Blockchain network to use for payment example: base required: - api_url - method Error: type: object properties: error: type: string description: Error message details: type: string description: Additional error details PaymentRequirements: type: object properties: scheme: type: string example: exact network: type: string example: base payTo: type: string description: Recipient address asset: type: string description: Token contract address maxAmountRequired: type: string description: Amount in microUSDC resource: type: string description: Resource URL description: type: string mimeType: type: string example: application/json maxTimeoutSeconds: type: number example: 180 ````