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invalid_token

401 Unauthorized   The access token is missing, malformed or expired.

When you get it

The access token is missing, malformed or expired. It is always answered with HTTP 401 - one code means one status, so a client may key its handling on either.

Fields it carries

Inside each errors[] entry, beside pointer:

reason

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

expiredAt

When the credential stopped being valid.

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

Present a valid access token (Authorization: Bearer …) or sign in. Re-minting the token is the usual fix.

Shape

{
  "type":   "https://api2.host-tracker.com/problems/invalid-token",
  "title":  "The access token is missing, malformed or expired.",
  "status": 401,
  "code":   "invalid_token",
  "errors": [
    { "reason": …, "expiredAt": … }
  ]
}