How to make server control client's rotation?

I’m making a multiplayer game and I need to be able to control the client’s rotation through the server. Ie, if I press X, then the client looks in the same direction as the server until, say, I press Y. I need this to be continual - so if the server looks up, the client looks up, the server looks right, the client looks right etc. At the moment I’ve got this working on the server; the client rotates in sync with the server. But on the client side he won’t rotate in sync, and then when he rotates on his own, it doesn’t show up on the server. Someone please help - I’ve tried everything!