Wow, thanks! Not trivial to get started at all.
Could you add an extra step in between 1) and 2)? After logging into graph.api.smartthings.com, click on “My Locations”, then your location name (mine is “Home”). Evidently there are multiple websites depending on world location and how many hubs they’ve sold. For example, clicking on “Home” takes me to graph-na04-useast2.api.smartthings.com. Only then can I follow the rest of the instructions and have it work. Before I did this step, everything appeared to work, but the CoRe smartapp never showed up on phone until I followed the link to my own special website.
This additional step should also be added to the wiki under “CoRe smartapp installation”, but I don’t have a login to request it. Maybe someone else could?