Rpc client issue

Hello,

I need your help to make an RPC function work. I have a button in Unity, onClick call this function :

     public void LaunchGame() {
             if (Network.connections.Length == 1 && Network.isServer) {
                 Debug.Log ("Game Starting...");
                 gameControllerGameObject.GetComponent<GameController> ().LaunchingGame ();
             } else {
                 Debug.Log ("You need to host a server with at least two players to start a game");
             }
         }

On the Gamecontroller script there is those 2 functions.

 public void LaunchingGame() {
         RpcLaunch ();
     }
 
     [ClientRpc]
     public void RpcLaunch () {
         testObject.GetComponent<Image> ().color = Color.blue;
     }

I tried with multiple way, with Command, NetworkIdentity or not on GameController and the Test Object. But I always get this error.

 RPC Function RpcLaunch called on client.
 UnityEngine.Debug:LogError(Object)
 GameController:CallRpcLaunch()
 GameController:LaunchingGame() (at Assets/Scripts/GameController.cs:36)
 UnityEngine.EventSystems.EventSystem:Update()

I already make a RpcClient function and it was working so I don't understand why this one doesn't work, I'm sure I missed a simple things.

Thank you.