Error with User Sync

I tried to sync users from one site to another, but I received message saying that there was error during the sync.
I'm not sure what the message said exactly, because the message is not appearing anymore.
Can I run it again and see the error message?
Can I turn the debug mode on and see the logged error?
I can't see the option in the plugin wordpress user sync
before the first sync, the option was there.