All error codes

invalid_json

HTTP 400 Request body is not valid JSON

What happened

The request body could not be parsed as JSON. Common causes are a trailing comma, a single-quoted string, an unescaped newline inside a string, or a truncated body.

What to do

Fix the body so it is valid JSON with an object at the top level, then send the request again.

Retrying

Fix the request and send it again.

How it arrives

{
    "type": "https://docs.fiberax.com/errors/invalid_json",
    "title": "Request body is not valid JSON",
    "status": 400,
    "code": "invalid_json",
    "request_id": "a277dcd1ca652c65"
}

Branch your code on code, never on the wording of title.