After enabling Wikibase client I see 'Add Links' link on the sidebar, but when I click it the browser blocks the request because it goes to some unsecure location "http://repo.example.org/w/api.php?action=query&format=json&origin=..."

I've found this reference in extensions/Wikibase/client/config/WikibaseClient.example.php file, tried to change it there, but it didn't help. It feels this address comes from DB but I didn't find it there either.

This only happens if I click this link. If I copy its address and enter to the browser, it works fine, because in this case I copy exactly what is inside the href attribute and this is a correct link.

Also this issue is only when I'm logged-in.