When you use :FireServer(), not only will it send the information attached to it, but also the player who the :FireServer() comes from. This helps the server to a get a better grasp of where it’s coming from, and can be of good use to secure RemoteEvents, & for other purposes if you want to implicate the player for something on the server. In this case, you could just add this into your Remote Script:
local iremote = game.ReplicatedStorage.invCont
iremote.OnServerEvent:Connect(function(plr, a, f) --This will let plr be the player argument, rather than a!
print(a, f)
end)