Having trouble subscribing [solved]

I'm trying to subscribe to https://lemmy.world/c/mst3k and https://feddit.de/c/raspberrypi , but I can't seem to subscribe to anything outside of vlemmy, lemmy.ml and beehaw.

I tried using the method in the "How to Join Lemmy" post, and the instructions on the page (ie. copy and paste "!mst3k@lemmy.world" in the search)

Am I doing it wrong, or is some type of server thing? I don't know how any of this works