If you purchased the application online, make sure you are logged in with the email you used for the purchase.
Next, ensure that you have the latest version of the application installed.
Then, go to the Profile page within the application, press the 'Restore Purchases' button under the Premium section at the bottom, and wait for 15-20 seconds.
If the Premium membership still hasn't been activated, try closing and reopening the application.
If the purchase was made through the App Store or Google Play Store, you need to log in with the account used for the purchase in the respective App Store or Google Play Store application on your phone to ensure that the data reaches our system