Make sure you’re signed into a Google account. Go to https://groups.google.com/g/mariocube/You will see a note saying “You don’t have permission to access this page”. This is normal.
Click “Join group”, and then click “Join group” again on the window that pops up. This is important. If you don't do this, you cannot access them. You will see a message saying “You don’t have permission to access this page” until you refresh.