Invalid sub template

What it means

The request was malformed, or a field failed validation.

Example detail messages returned with this error:

• ‘sub_claim_template’ must be null or a string ≤ 256 chars.

What to do

Correct the sub_template value - detail names what was wrong.

Response shape

All fremforge API errors are RFC 9457 problem+json:

{
  "type": "https://docs.frem.sh/reference/api/errors/invalid-sub-template",
  "title": "Bad Request",
  "status": 400,
  "detail": "..."
}

Branch on type, not on title or detail - those are human-readable and may be reworded.