Google Play payment option not supported?

Whenever I try to make a purchase using Google play, I get an error message saying that the payment method is not supported. I know that it is supported, as I have been using Google play as a payment method for a while now. Any help I could get on this would be appreciated.

Staff here already have said on other threads about Google Pay that the Gameflip engineers are looking into it.

Don’t think Google Play (or iTunes) payment will be supported. These payment methods are for purchasing apps or items within a game app. Google & Apple takes 30% from such transaction. Imagine you make a deposit of $10, and Google takes $3 immediately. That wouldn’t work, right?