Core not working on second account

Hello… I have a fully functional and 100% great smartthings location including lots of working Core pistons. I recently created a new account in my mom’s name with no ST hub, and the only device is her phone as a presence sensor. I installed Core in her IDE and everything looks right, except that when I tap Add a Core piston I get the spinner and nothing more. The Core smartapp is published, OAuth is true, I updated it from the Github repository, it should work. Is it possible that it required a hub at the location?