Syncs, but "Running (Offline)" and missing API key

Fresh 1.2.2 installation on a brand new OSX machine (Mojave). Connected to three other OSX machines (ostensibly) on the same local network.

Syncthing in the menu bar, however, will only ever show as “Offline (Running)” (with an amber dot). How do I get this to “Online” (green)? Any help appreciated.

And don’t know if this is related, but under Preferences the is API Key field is empty (and “Test” with a red dot). There is an API Key shown in General Settings in the GUI, and I’ve tried regenerating and copying into the field in Preferences, but nothing has gotten the API Key to stick there.