I bought a duplicate player and when I went to rank him up it didn't work and I

Rank up have chances to fail or to succeed now.

For the first 1 or 2 rank up I think you need 1 player to rank them up, then after the 2nd rank up, the 3rd rank up and so on needs 2 or more duplicates of the same card for the success rate to go up like 25% 50% 80% something like that according to how many duplicates you've added, and it also does in fact make your purchased players gone after a failed rank up and you cannot get them back.

So it's better for now to (unless EA revamps the rank up system.) buy cheaper Bronze/Silver cards to rank them up and use them for matches cuz they're OP.

But if you want higher OVR, I guess buy the players you want that's expensive then just rank them up 1 or 2 times if you're scared to rank them up higher and lose the duplicates you bought for crazy amount of coins.