All in-app transactions are directly handled by Google (for Android devices) and Apple (for iOS devices). The game developers do not have any influence over what payment methods are accepted by Google or by Apple.
iOS (App Store)
For information on purchasing methods, please refer to this link:https://support.apple.com/en-us/HT202631
Android (Google Play)
For information on available purchasing methods, please refer to this link:https://support.google.com/googleplay/answer/2651410?hl=en