I am gunned guns
And improvements like more Safety, life and energy
And also selling ammunition
The sales system is a help service to have more space because I have been able to sell only 6 objects
Lebrando that is with money inside the game
I don't understand everything but from what I can piece together you already have in-game currency?
So you want players to be able to buy your in-game coins using real money? Am I correct?
First set your in-game money (currency) and use the IAP plugin to give the player an option to buy more. You should check out tutorials on the IAP plugin because there are different types of purchases in iOS and Android.
The in-game selling part is easy enough.
For Life (HP), Defence (Safety), Energy (I'm assuming this is like MP) all you need to do is set the price of the increase the maximum values of the said quantities (Life, Defense, Energy) when the player touches the buy button (assuming the player has enough of the in-game currency to afford them.)
For the guns part, simply lock the guns you want to sell until the player is able to afford. By the way, have you been able to implement all features ? Do you already have a working game?