Just to clarify, once you’ve added those ‘Additional Devices’ selections via the SmartThings Mobile app, those devices should automatically show up in SharpTools.
In other words, you don’t need to go back through the authorization process starting from your SharpTools.io User Page. If you do, the more limited set of authorizations from the web authorization flow override the ones from the mobile app (it’s a bit of a quirk with the SmartThings authorization flow).