/v1 endpoints return an Error object. The token endpoint,
/oauth/token, returns OAuth 2.0 errors (error and error_description)
instead. A request body that is over 10 MB or can’t be read gets a plain
4xx response without an Error object.
Its code identifies the error and doc_url links to the page for that code
below.
When a validation error is about specific parameters, invalid-params lists
them.
With an Idempotency-Key, most 4xx responses are stored and replayed for
at least 24 hours. After fixing the request, send it with a new key.
request_id when you contact support.