While this is under Google control as explained above, there is something that 90% of the times solves this issue: Enter Play Store app, go to settings and remove your payment method data, then add it again. After that, try the purchase.
If it still fails, please make a small test: open any other app with in-app purchase and check if you can initiate a purchase. You don't have to actually buy anything, just check if you see the first "prompt window" from Google showing the price, payment methods available, etc. My guess is, it will fail with all other apps as well.