If you perform a PATCH operation to update a field that is marked as "read only", the API call will return a 204 No Content.  The content is not updated, but the end user is wondering why.  This is a misleading response and causes a lot of confusion.

There are a number of different open bug/suggestion tickets tied to individual endpoints and field updates failing with a 204, but the common theme among all of these is that the fields are flagged as read-only in the DTO schema.  The API should be updated so that a proper error message is returned if a read only field is attempted to be updated.