So in mobile phone Game (Android, iOS), PC game, how to implement that (title)?
In game, game company's specific crypto currency's address, QR code appears for payment receiving,
gamers see that, and send amount to that address, it should be automatically recognize and when it confirmed, game should automatically give item to users.
How this be done technically behind the scene?
In real world you really shouldn't. It's way easier and convenient for most games to create non-tradable currency because if it was tradable devs should have to deal with in-game economy. That's why you almost never can giveaway or trade "diamonds" in games like clash of clans and other mobile games.
In game currency does not need insane robustness and fraud protection so it's much more effective to store it in SQL rather then in some super complicated structure like Blockchain.
The only viable application for blockchain I see for in-game currency is cross-developer currency that works and tradable between different games of different developers. Still the rules of it's creation should be defined very carefully.
TL/DR - you don't need to introduce real life economy in time-killer game.