Otherwise, here are some things to check:
Special Information for Purchases Prior to December 2014:
For purchases made prior to the release of version 3, in December 2014, a separate license "app" was purchased from Google Play or Amazon and installed on your device to unlock the program. If you have not upgraded this to an in-app purchase, then check to make sure that you have either "Ultimate To-Do List License" or "Ultimate ToDo List Tab License" (depending on what you purchased) installed on your device. If the license app is not there, you should be able to download it from Google Play at no charge, as long as your device is linked to the same Google account as your original purchase.
Once you have verified that the license app is install, it may be necessary to reboot your device to force Ultimate To-Do List to perform a license check and unlock itself.