I've downloaded version 4. I open it and select Back up/Restore. I get a dialogue box saying "full version required". I press "Upgrade". Button says "upgrade from stagetraxx 3", $14.99. I press "upgrade". New App Store box appears, with button on lower right of screen saying "double click to pay". I double press it, but nothing happens. No notification about my purchase, and still can't restore my backup from Stagetraxx 3.