Errors & status codes

Status	Meaning	Typical `error`
`200`	OK	—
`201`	Created (instance created, order placed, key created)	—
`400`	Bad request — missing/invalid fields, instance not `RUNNING`, no runner assigned, invalid JSON	`Missing required fields: symbol, type, volume`
`401`	Auth failed — missing/invalid/inactive/expired key, suspended account, no credits	`Invalid API key` / `Account has no credits remaining`
`403`	Forbidden — instance limit reached, accessing another account's resource	`Instance limit reached (5)`
`404`	Not found — instance/order/position/key not found or not yours	`Instance not found`
`409`	Conflict — instance already exists, connection state conflict	`An instance with this account ID already exists`
`500`	Internal error	`Failed to place order`
`503`	Service unavailable — no available runner, or the runner is offline	`Runner is not connected`
`504`	Gateway timeout — runner accepted the command but didn't respond in time (outcome unknown)	`Broker request timed out…`

Important on 504: for order placement, a 504 means the command reached the runner but no response came back within the timeout. The order may have executed. Do not blindly retry — reconcile via get positions / get orders first, or send every order write with an Idempotency-Key and retry with the same key.