x402 quickstart - Compose.Market

Start most integrations with a Compose Key. Raw x402 ‘upto’ is great for agentic / a2a workflows, cause Manowar agents control a wallet and can handle a 402 Payment Required retry flow natively.

Call with a Compose Key

Use this for servers, scripts, IDEs, and OpenAI-compatible apps.

curl https://api.compose.market/v1/chat/completions \
  -H "Authorization: Bearer $COMPOSE_MARKET_API_KEY" \
  -H "Content-Type: application/json" \
  -H "x-chain-id: 43113" \
  -d '{
    "model": "gpt-4o",
    "messages": [
      { "role": "user", "content": "Explain x402 in one sentence." }
    ]
  }'

If you are configuring an IDE or app that expects an OpenAI-compatible base URL, use /external/v1:

curl https://api.compose.market/external/v1/chat/completions \
  -H "Authorization: Bearer $COMPOSE_MARKET_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.5",
    "messages": [
      { "role": "user", "content": "Hello from an external client." }
    ]
  }'

External responses keep the OpenAI shape because many external tools reject unknown fields.

Call with raw x402

Raw x402 has two requests. First, send the request without PAYMENT-SIGNATURE:

curl -i https://api.compose.market/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "x-chain-id: 43113" \
  -d '{
    "model": "gpt-5.5",
    "messages": [
      { "role": "user", "content": "Price this request." }
    ]
  }'

The API returns 402 Payment Required and a PAYMENT-REQUIRED header. Sign that requirement with your x402 client, then retry:

curl https://api.compose.market/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "x-chain-id: 43113" \
  -H "PAYMENT-SIGNATURE: $PAYMENT_SIGNATURE" \
  -d '{
    "model": "gpt-5.5",
    "messages": [
      { "role": "user", "content": "Run the paid request." }
    ]
  }'

For usage-priced calls, add x-x402-max-amount-wei to set your own cap:

-H "x-x402-max-amount-wei: 1000000"

Amounts are USDC atomic units. 1000000 is 1 USDC.

Common failures

Status	Meaning	What to check
`400`	Request shape is invalid.	Body JSON, model ID, modality, or metering input.
`401`	Auth failed.	Missing, expired, revoked, or malformed Compose Key.
`402`	Payment failed.	Missing x402 signature, exhausted budget, insufficient allowance, or settlement failure.
`429`	Rate limit.	Retry with backoff. Provider limits can surface here too.

​Call with a Compose Key

​Call with raw x402

​Common failures

​Related

Call with a Compose Key

Call with raw x402

Common failures

Related