Thank you Zach, for all your help! The reason calling the GET “off the bat” doesn’t make much sense is because this page/exchange is made up of a whole bunch of calls/data, in which the data retrieved by the GET doesn’t exist until the user has done a bunch of stuff on page and made a POST to that service end point, until then there isn’t any “bill object” to return. Nothing is actually even persisted by this exchange, so initialising the page and calling the GET will just turn up nothing. I hope perhaps that makes some sense, it’s complicated (of course!).
But to the problem! It appears it is solved! I don’t know if this is working-as-designed, but you don’t get the Data Source Options on the model if the REST Model is defined as Read/Write. Only if it is “Read Only”
Having applied your advice above, and then out of clicking-frustration, I changed the REST model to be read only, and suddenly the Data Source fields appear at the model level (and obviously the ability to define other methods on this model disappear, as they are all Write based methodologies).
If I stick my service resource location in there, and leave it as GET - the field list suddenly shoots out all the fields in my return type - as you expected!
If I flip this back to “Model Behavior = Read/Write” then the two inputs above disappear, and I am returned to adding methods to the model myself.
and
right?
However, all the fields remain - which kinda makes sense, once they are in the XML I’d be surprised if that would make a bunch of destructive changes.
Spurred on by this sudden success I have been back round and round the houses trying to get the Read/Write behavior to pull the fields out again, but I simply cannot configure a Method that does it.
I can get it back every time when I flip it to Read mode.
I wonder then if you can confirm - that’s how it’s supposed to work? I can’t think why it wouldn’t want to do the field detection if you wanted a Read/Write REST model, it could still just use the Query method - and it’s really just a convenience that it does this, you can still manually add and remove fields?
If this isn’t what we’d expect, I’m using Skuid v12.0.1 and I’m happy to document/recreate this in as much detail as might be helpful 
