• 401 unauthorized: the key is missing, mistyped or revoked. Send it as the header Authorization: Bearer YOUR_KEY.
• 403 forbidden: the key is not allowed to do this. A leads-only key cannot read; a read-only key cannot change anything; a key limited to some parts of the account cannot use the others. Create a key with the right level under Account, Integrations.
• 404 not_found: no record with that id exists in your account.
• 409: the change conflicts with something: an email already used by another contact, a contact that still has deals, a board rule such as open subtasks, or a product your company does not have.
• 422 invalid: a field is missing or not accepted. The message names the field.
• 429 rate_limited: more than 120 calls in a minute. Wait a minute.

The full reference is at https://work.spotbookr.com/developers.