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malformed_request

400 Bad Request   The request could not be parsed.

When you get it

The request could not be parsed. It is always answered with HTTP 400 - one code means one status, so a client may key its handling on either.

Fields it carries

Inside each errors[] entry, beside pointer:

pointer

RFC 6901 JSON Pointer to the offending value in the request body.

detail

Human-readable detail for this one occurrence. Never the only place remediation appears.

reason

The machine-readable sub-case, when one code covers several. Branch on it.

A field is omitted when the server genuinely does not know it - an absent member is never the same as an empty one.

How to fix it

The request could not be parsed. Fix the syntax - this is not a permissions or state problem.

Shape

{
  "type":   "https://api2.host-tracker.com/problems/malformed-request",
  "title":  "The request could not be parsed.",
  "status": 400,
  "code":   "malformed_request",
  "errors": [
    { "pointer": …, "detail": …, "reason": … }
  ]
}