Switch Can't join multiplayer on Nintendo Switch

[The Azu Cafe System]

I wanted to play Terraria on a multiplayer world with my gf, but when she tried to join me, it said "fail to join" (something like that), so we tried a few more times, and the error persisted. She tried connecting to a different wifi source, which didn't help either. I tried joining one of her worlds, and it said the same "fail to join" message.

We both do have switch online, so that is not the issue. I'm wondering if servers are down or if we just can't play together. I appreciate any help!