Some ways of paying finish outside the game: paying cash at a shop, for example, or a purchase waiting for a parent or family manager to approve it. Google Play reports these as pending, and the game waits until the payment has actually cleared before it unlocks anything.

While you wait, the purchase window says Your payment is still being processed. There is nothing else you need to do. When Google confirms the payment, the full game opens by itself: straight away if the game is open, or the next time you open it.

If the payment is cancelled, or never completes, nothing in the game changes.