So im still not sure what you was asking. There is no bank page. In the shop you can use real cash to buy currencies (gems, viagra, and bucks). I havent spent a cent so i dont know the exact steps, but i have spent money on other games before, so its pretty simple:
1. Pick what you want to buy (both type of item and quantity. The price should be clearly visible)
2. Enter credit card info
3. Loads a confirmation screen and you go back to the game screen, with your newly added funds.
Thanks for pointing out that change for gem gacha. Im not gonna be able to purchase that one any time soon. Because of that, im pretty sure alot of people will drop playing this game. I will still be vigilant.