Photon and Unity : Up down character movement when the seconde player join

Zefix

I'm currently experimenting with photon in Unity and I'm trying to work with mouse click movement with an up down environment but I got an issue with that.

I can connect multiple players in the same room. The first one can move and the camera follow the player prefab as I would like to work.

But when the second player join the room, he is not able to move is character and I don't know why.

Here's my game manager script:

My player prefab is being instantiated when the players click on a button "Start".

Here's my character movement script if you need it:

Thanks for the help, really appreciated!

I'm new to Unity so any advice will be helpful