Can someone please give me some advice?

So I have a tumblr account and I posted a short fanfic story on there a few months ago, but recently an account about the show that I wrote the fanfic for, read my fanfic and recommended it to some of their friends.
They’ve now asked me to join them on ao3 and discord. I really like this account and I’d like to, like stay in touch with them? (We haven’t really talked that much but I’d like to be friends with them) But I’m not really comfortable with making an ao3/discord account and I really don’t want to sound rude to this person.

Does anyone have any idea about how I could tell them that I don’t want to join but I’d like to still like to talk to them without sounding rude?
Thanks, any help will be greatly appreciated.