Finally we know why Threads doesn't federate with metalhead.club: We are "violating the community guidelines or terms of use!"
I can't do it anymore! I CAN'T DO IT ANYMORE! *hysterical laughter*
Well that ends the issue. I haven't gotten a response even after many good-natured attempts to contact threads/meta and I'm tired of begging. If they don't like it, let them be without us. Too bad (because one or the other user would probably have read threads), but that's not going to happen.