Status codes

Status	When	Sparrow-style senders
200 OK	Captured in server mode with the default response	Success
202 Accepted	Captured in browser mode, or a browser-mode response handler didn’t answer in 10 s	Success
your status	A response handler or a sync forward target set it	Depends on the status
400 Bad Request	The slug has invalid characters	No retry
401 Unauthorized	Signature enforcement is on and the signature is missing or invalid	No retry
404 Not Found	No endpoint has that slug	No retry
413 Payload Too Large	The body exceeds MAX_BODY_SIZE	No retry
429 Too Many Requests	The client IP is over the rate limit; includes Retry-After: 1	Retries later
502 Bad Gateway	A sync forward got no response from the target	Retries
503 Service Unavailable	The database is unreachable	Retries

The default response body is:

{"status":"ok","id":"<request id>"}

Retry behaviour varies by sender. Many, including Sparrow, retry 5xx and 429 but treat other 4xx responses as permanent failures, which is why a database outage returns 503 rather than 404.