handle_reserved
409 · Conflicts with the current stateWhat happened
That handle is held back and cannot be claimed. Which ones, and why, is deliberately not said: naming the rule would name the handles worth trying next.
What to do
Pick another.
Is retrying worth it
No. Repeating the identical request will fail identically. Something has to change first, and the line above says what.
Reading the response
Errors are RFC 9457 problem details. Switch on code, which is stable, and never on title, which is written for a person and may be reworded or translated. detail carries the specifics of this occurrence, and meta carries whatever the client needs to render the right state instead of a dead end.
Every response also carries an X-Request-Id header. Quote it if you report something — it is what lets us find the exact request.