How to sync material change at runtime - unet ?

Hi I'm trying to sync a material change among players(clients) without any succes so far, the player's material have to change as soon as the player is spawned. Here my code:

 public class playerMaterialSync : NetworkBehaviour {
 
 
     [SyncVar]
     private Material syncMaterial;
 
 
     void Start () {
 
             StartCoroutine (CoolDown (2.0f));
          
     }
 
     void ChangeMaterial(){
         if (!isLocalPlayer) {
             GetComponentInChildren<MeshRenderer>().material=syncMaterial;
         }
     }
 
     [Command]
     void CmdSendMaterialToServer(Material mat){
         syncMaterial = mat;
     }
 
     [ClientCallback]
     void TransmitMaterial(){
         if (isLocalPlayer) {
             CmdSendMaterialToServer(GetComponentInChildren<MeshRenderer>().material);
         }
     }
     IEnumerator CoolDown(float waitTime){
         yield return new WaitForSeconds (waitTime);
         TransmitMaterial ();
         ChangeMaterial ();
     }
 
 }