FREE_FLOW_BUSY

This sender already has a free transaction in flight.

HTTP status	409
Group	Relay path
Retryable	Yes — the same request may be sent again
Re-sign	SAME_BYTES — resend the transaction you already have, byte for byte

What happened

The free flow allows one non-terminal free intent per sender, at the on-chain nonce with an empty pool, so it cannot be used to drain gas.

What to do

Wait for the free intent to settle, then send the next one.

Extra members

This code carries reason in the problem document, on top of the common members.

The problem document

Every error is application/problem+json (RFC 9457) with the same shape:

{
  "type": "https://docs.co-relayer.com/errors/free-flow-busy",
  "title": "This sender already has a free transaction in flight.",
  "status": 409,
  "detail": "A sentence about this specific occurrence.",
  "instance": "req_01JB…",
  "code": "FREE_FLOW_BUSY",
  "retryable": true,
  "resign": "SAME_BYTES",
  "hint": "Wait for the free intent to settle, then send the next one."
}

See the error model for what each member means and how to handle unknown codes.