Cannot make another developer access private repo via git

I have a private repository here.

I can clone it and do standard git things with no issues via ssh.

I invited another user, the user accepted the invitation and I set his role to owner.

I can see in members table this user with owner role.

The user has account on gitlab, with ssh auth, and do standard things OK. For example he can clone non private repo just OK.

However, when he tries to git clone the private repo I gave access to, it says permission denied or repository does not exists.

I thought to add his pub key as deployment key, but it’s not possible as same key already used.

The user uses git for windows and operate from git bash terminal.

It works properly with repositories.

Where can be the problem?