I can't complete my purchase. The Google Play message says, "You already own this item"

Please try the following:

1. Check that you are logged into the same Google Play account which you used to make your original purchases.
2. Ensure you have the latest update for the game
3. Ensure you have the latest operating system for your device
4. from Google support page:

Clear the cache & data of the Play Store

This gives the app a fresh start and can help fix issues.

1. On your Android phone or tablet, open the Settings app .
2. Tap Apps & notifications  See all apps.
3. Scroll down and tap Google Play Store .
4. Tap Storage  Clear Cache.
5. Tap Clear data.
6. Re-open the Play Store, and try your download again.