If you created a subscription or if you have been charged for a renewal and have not yet seen the currency in your account within 24 hours, you may need to clear your game data.   After doing so, your credits should arrive.

You can clear your game data in Android's Application manager:

From your devices' Settings screen, find the section that shows "Apps" or "Application Manager." (it varies according to device and operating system version.)

Among the apps listed in your Apps Manager, find this game and select it.  You should see an option to "Clear Data." Your subscription credits should now show.

Please note that this fix applies to this specific title and should not be attempted for other apps or games.