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idempotency_key_required

400 Bad Request   This operation requires an Idempotency-Key header.

When you get it

This operation requires an Idempotency-Key header. 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:

endpoint

The operation the rule applies to.

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

Nothing is wrong with the request body. This operation requires an `Idempotency-Key` header - send one and retry. Use a fresh unique value (a UUID is ideal) per logical operation, and reuse that same value if you have to retry the operation itself, which is what makes the retry safe.

Shape

{
  "type":   "https://api2.host-tracker.com/problems/idempotency-key-required",
  "title":  "This operation requires an Idempotency-Key header.",
  "status": 400,
  "code":   "idempotency_key_required",
  "errors": [
    { "endpoint": … }
  ]
}