My friend gave me a digital copy of the game a few days ago I downloaded and I've been trying the code I got from my friend and it says this Serial key is invalid, so where do I get this online serial key at?

And please if any one can tell me I would be grateful

Go to Origin Client and redeem it there. It should work. Or, have EA call you and you can tell them key if you can't redeem it on origin client they will give you a new one. Steam keys are different so won't work on steam but you can redeem steam EA games on origin so no need to buy it but why redeem same copy on origin? Good news is that if you want to remove it, they can only remove from origin and you will still be able to use steam key on steam.