synchronization of objects

Hello,
I am creating a multiplayer with photon PUN. I already managed to sync the headset and controller. Now I want to sync a cube. The players should be able to pick the cube up and the other players should see the movement of the cube. I tried to create a cube with a script to interact with it (this works fine) and than I just added Photon View and Transform View (in the observe field) to sync position and rotation.
The result is, that only the master host (the first one joining the room) can interact with the cube and the other one sees it, but when the second one interacts with the cube, the first one does not see any movement. I tried to put the interactable Item script in the observe field of photon view, but than I get the error "The observed monobehaviour cube of this PhotonView does not implement OnPhotonSerializeView()!". What components does an interactable object need in the scripts to be observed by PhotonView?

I also tried the OnPhotonSerializeView(PhotonStream stream, PhotonMessageInfo info) method, this did not work either.

Any solutions ideas or completely different options to sync an interactable object over the photon PUN Network?

Please explain in easy steps, because I am totally new in programming and VR
Thx