Franz
Ok,I think I've figured out the problem. It seems that the REST API does not honor the user's group permissions. For example, my main board (which uses vBulletin) I have closed to the public, so for my Flarum test board, I mimic that privacy. So, I had this set in the Admin settings:
And even tho the user I was logging in as had permission to see everything, if I logged in with that user through the REST API, several of the REST calls were not working (some were returning 401, others were returning "{ data: [0] }").
Once I changed that setting to "Everyone", the REST API worked. This sounds like a bug, correct? (I can log it in GitHub if you'd like)....
And also, yes, yes yes! Please implement a way to list tags! 🙂