It's based on markdown. Here's two ways you can write the link:
!flask@lemm.ee
[!flask@lemm.ee](https://lemm.ee/c/flask)
The first one is a link that goes to the community from your current instance, which is handy. E.g. when I click it, I'll go to https://discuss.online/c/flask@lemm.ee. If someone on lemmy.world clicks it, they'll go to https://lemmy.world/c/flask@lemm.ee. This format is specific to Lemmy, but is similar to reddit's /r/flask
syntax.
The second link is a regular markdown link, and has the general format of [regular text](some url). This will always go straight to the URL, and won't have the above behavior. Generally for linking stuff like this, the first option is preferred.
All that said, to answer your question, I think you just typo'ed the URL. You typed lemm.me
(extra m
) instead of lemm.ee