@halcyon I did some checking and it turns out that at first I wasn't entering the instance correctly.
Still, for many instances I get a message that says "An error occurred, there was an error and Halcyon couldn't fetch or validate a access token for this instance" (which is improper grammar btw, it should say "an access token"), despite the fact that it kicks me to the instance page asking for my authorization.
are you doing
@username@instance
or
username@instance.
for halcyon i found that it needs to be @username@instance