Cannot complete purchase within an app

Unable to complete purchase. After clicking on item to buy in game a Screen comes up to click purchase. I click purchase, then screen says enter password. After enter password the screen will show 'done' for a split second, too fast to screen shot. Then the screen will show the game again briefly, then loop back to the 'purchase' screen. Just keeps looping To purchase, then password, then done, then purchase to password, etc.

No purchase is ever actually completed.