Below are some steps that usually help fix various billing errors:

Android
Please make sure that all billing settings are in order:
1. Ensure that you're logged into your Google Play Games account. Try to log out and log back in.
2. Ensure that you have the latest version of Google Play installed.
3. Check that you have sufficient funds in your account.
4. Go to Settings > Apps & Notifications, then find the Google Play Store app.
5. Tap on Storage > Clear Cache and Clear Data. 

iOS
Please make sure that all billing settings are in order:
1. Ensure that you're logged in using the same Apple ID that you used to download the game (Settings > iTunes & App Store). Try to log out and log back in.
2. Ensure that in-app purchases are allowed on your device (Settings > Screen Time > Content & Privacy Restrictions).
3. Check that your payment information is up to date (https://support.apple.com/en-us/HT201266) and you have sufficient funds.

Windows
Please make sure that all billing settings are in order:
1. Ensure you're logged in to your Microsoft account. Try to log out and log back in.
2. Check that your payment information is up to date and you have sufficient funds.
Note: If you receive a ""pending transaction"" error, it means that one of your previous transactions has not yet been completed. Please try to make your purchase again later.