YouTrack GitHub integration problem

Hellou!

I'm trying to integrate my project in InCloud Youtrack with my public repository on GitHub.
I generated OAuth Token on GH and put it to YT, then I set everything else to default values (owner to me, commiters to all users, all monitor branches (empty textbox) and visible for all (empty ddl)).
When I click on Save button, I get error message "Unable to perform operation" and nothing more.
I have no idea, where is problem. Do you have any suggestions?

Thank you,
Jan K.