How do class trainers work ?

Hey there folks,
I was trying to place some class trainers down so my lvl2 players can access their new abbilty’s. But after some waiting i kept on seeying how no player got any training and i don’t understand why. I have a trainer for every class and i placed them around places where players lvl up regurarely but i still have no result.
Could someone maybe explain me what im doing wrong?