Your server is not supporting BUD-04 spec. This is why mirroring is not working. Primal app is hitting your server with `PUT /mirror` and gets 404 as response. You have to update your server with BUD-04 if you want this to work.
Discussion
Yup, i followed that. Going to submit an issue (or multiple) later and look at source to see if i can be useful (doubtful)