I now trying to build a logic where player after collecting some "coins" can go to the upgrade page (shop) and use them for different upgrades.
Default player health at first launch of the game is: 10/100
You can upgrade to 20/100 by spending 20 coins.
Next round of upgrade to 30/100 by spending 50 coins. So that amount of money is increasing.
If coins is not enough, he can buy some with real money.
This all upgrades are stored/saved for the next time user plays the game.