[ Staff Help Required ] How do I get in game microtransactions to work in my multiplayer game via Steam or Epic Store?

What are the things I need to do to get microtransactions to get working within my game? for example a player who has bought my game now wants to purchase a gun that costs $2.50 , how will that gun ( a DLC ) transfer into the account of the player who has bought it and can then access that gun in the game?

Also another important question - Does Epic Games provide user accounts for a multiplayer game? like lets say a player account where all the stats of the players kill count, K/D Ratio , is stored, or even store the DLC content bought by the player? ( just like a PSN account )