bad-request
HTTP 400 Bad Request
The request sends Content-Type: application/json, but the body is not valid JSON, so the API cannot read it. Typical causes are a trailing comma, single quotes, an unescaped line break, a truncated body or an empty body. detail stays generic on purpose and never repeats the body.
Fix
Serialize the body with a JSON library (JSON.stringify, json.dumps) instead of assembling it as a string, and send Content-Type: application/json only together with a JSON body. A body that is valid JSON but has missing or wrong fields answers validation instead.
{ "type": "https://docs.qr3.app/errors/bad-request", "title": "Bad Request", "status": 400, "detail": "The request could not be processed"}