How do i do this objective?

Hey i'm pretty new to fifa games so i might not know a lot. This is one thing that has me scratching my head. I am playing manager career mode as a Liverpool manager and i have this one objective that i have no idea on how to complete (see attached screenshot). Anyone have any idea how i can do this? Its an objective called Youth Development and it tells me to: Sign at least 2 players younger then 20 with greater potential then somone already playing in that position. 

I have done everything logical to try and get this done, i've signed like 3-4 new players that are all 90+ potential yet it doesn't seem to work. I have even already promoted one of these to the first team but that didn't help either. Help is appreciated.