I think it is not needed to provide a valid id here. In the Mendix appstore widgets it is not used, as far as I know. Probably just an id.
What I have discovered is that in a Mendix Widget like the data grid the id is linked to the first attribute in the grid and it causes the return json to only bring back the primary entity and no associated entities. That is my goal. I have tried to use depth of 0, -1, 1 but to no avail however bif I copy and past a id into one of my calls and using fiddler resend the call I get and error that states that the entity does not have that specific attribute and that the depth is -1.
At the moment some of the calls from or widget are bringing back the whole data model related to the entity you want which causes a lot more traffic that we need.
Any help would be appreciated