Safari extension doesn't work

Whenever I try to import any lesson, I get this message (see the shot screen).
I’ve tried to reinstall the Safari extension several times, but it didn’t work.
I’m desperate, this problem occurred, after I’d upgraded my Macbook to mas ox Catalina (10.15).
Does anyone have a similar problem? Any suggestion?

Sorry to hear that!
Can you send us links to articles/videos you tried to import with extension but didn’t worked?
Also lesson URL would be great too.

Have you tried to refresh the page? Does lesson show up eventually later?