I'm testing using Group Activities and having no trouble iOS<->iOS or starting an activity on macOS and joining via iOS. However, when I start an activity and then try to join it from another macOS client, the starting side joins the session just fine, but the receiving side acts like I don't have the required app, even when it is already running.
I see the active SharePlay icon in the menu bar, and the Current Activity is shown, but instead of an "Open" button there is a "MyApp Required" string and a "View" button that goes to the App Store. (Where the app is not available yet, as expected, since I'm still working on it.) There is no GroupSession started on that Mac yet, obviously.
I'm looking for any hints to help debug what is going on. How does Group Activities find the app for the activity on macOS and how can I figure out why it isn't finding mine?
Thanks!