Sometimes the Play Store itself loses track of the purchase: Clear the cache and data for the app.
In Hex Installer, go to the section > Fix HC Base and delete the High Contrast base.
The most effective community-verified fix for One UI 5 users is to completely remove the Secure Folder. hex installer apk license error
Go to > Security and privacy (or Biometrics and security). Select Secure Folder > More settings . Choose Uninstall .
On One UI 5 and later, the presence of the Secure Folder often blocks the app's license verification. Sometimes the Play Store itself loses track of
Re-download the High Contrast theme from the store and try re-applying your Hex theme. 3. Refresh Play Store Identity
If the app opens but themes won't apply, resetting the base theme can help: Apply the in the Galaxy Themes app. Go to > Security and privacy (or Biometrics and security)
If the app was sideloaded as an APK rather than installed directly from the Play Store, the license verification will naturally fail. How to Fix Hex Installer License Errors 1. Uninstall Secure Folder