type: string
description: |
  The error message should help users understand and resolve the API error easily and quickly.
  In general, consider the following guidelines when writing error messages:

  - Do not assume the user is an expert user of your API.
    Users could be client developers, operations people, IT staff, or end-users of apps.
  - Do not assume the user knows anything about your service implementation or is familiar with the context of the errors (such as log analysis).
  - When possible,
    error messages should be constructed such that a technical user (but not necessarily a developer of your API) can respond to the error and correct it.
  - Keep the error message brief.
    If needed, provide a link where a confused reader can ask questions,
    give feedback, or get more information that doesn't cleanly fit in an error message.
    Otherwise, use the details field to expand.

  [Reference](https://cloud.google.com/apis/design/errors#error_messages)