The pro version is no standalone app. Its an in-app-purchase that enables additional features that where previously locked.
You can see this when the button “Upgrade to pro version” disappeared and those additional pro-features should be enabled, like XLS-Export/Import, attachment of images etc.
If the app nonetheless wont identify pro license it may can have several reasons.
The app gets its license state from Google Play services. Google Play services are caching licensing states, but sometimes this leads to problems. In most cases its enough to do a restart, because the cache will be cleared on reboot. After reboot the app should recognize pro state.
If it still does not recognize after reboot, make sure you installed app via the account that made the purchase (select the account in the left navigation drawer in Google Play, then install the app).
If you face issues with multiple Google accounts please contact me via email.
IMPORTANT: Before reinstalling with another Google account do a Backup of your database first!