Cant move after Pawn Possess (client server game)

I´m building a asymmetrical game were player 1 gets one pawn and player 2 gets an other pawn.
At the movement i don´t know how and were I have to Possess the pawn to make it work and even if the players get the correct pawns, the client cant move. The client moves a litle bit and than jumps back to its original start possition.
I have no Idea what to do now, i´m thankfull for sugestions

your char is replicated? have you possessed server side? show some blueprint screenshots so we can see what you did there.