HTTPayer Relay API Specification

Table of Contents

Overview

The HTTPayer Relay Server is a privacy-first payment proxy that enables you to pay for x402-compatible APIs with cryptocurrency without revealing your identity to the target API.

For documentation on API specs, visit HTTPayer Relay API Specification.

Key Features

✅ Privacy-Preserving: You pay HTTPayer (not the target API directly) ✅ Cross-Chain Support: Pay with Base USDC for Solana APIs, or vice versa ✅ Verified Payments: HTTPayer polls blockchain to confirm payments before charging you ✅ Fair Billing: You are only charged if HTTPayer successfully pays the target API ✅ Automatic Retries: Handles payment processing latency gracefully (sync + async) ✅ Flat-Rate Fee: 10% relay fee

Base URL

Production: <https://api.httpayer.com/>

Payment Routes

HTTPayer supports 4 payment routes covering all combinations of EVM (Base) and Solana chains:

Route User Pays With Target API Accepts Cross-Chain? Supported Networks
1. EVM → EVM Base USDC Base USDC ❌ No base, base-sepolia
2. Solana → Solana Solana USDC Solana USDC ❌ No solana, solana-devnet
3. EVM → Solana Base USDC Solana USDC ✅ Yes Any EVM → Any Solana
4. Solana → EVM Solana USDC Base USDC ✅ Yes Any Solana → Any EVM

How It Works

┌──────────┐                ┌──────────────┐                ┌──────────┐
│   You    │   X-PAYMENT    │   HTTPayer   │   X-PAYMENT    │  Target  │
│ (Client) │ ─────────────► │    Relay     │ ─────────────► │   API    │
└──────────┘                └──────────────┘                └──────────┘
                                    │
                            ┌───────▼────────┐
                            │  Blockchain    │
                            │  Verification  │
                            └────────────────┘

Payment Flow:

  1. You request API without payment → Get 402 with HTTPayer payment instructions