Use this endpoint to add new Shifts to an existing Event. The advantages of this endpoint over the Update endpoint are that you needn’t know the other properties of an event and it will return the unique identifier of the new Shift.
If the specified Event does not exist, this endpoint will return an error with HTTP Status Code
404 Not Found.
If the specified Event does exist but is not editable, this endpoint will return an error with HTTP Status Code
If successful, the endpoint responds with HTTP Status Code
201 Created and the integer ID of the created Shift in the response body.