Trying to send command object without authority

Hello , im trying to implement a simple chat in TPS multiplayer game , when playing as host , the chat works perfect , but in client it tells " Trying to send command object without authority " , i've looked on every answer and none of them fix my problem , can anyone help me ? thanks .

Heres the code :

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UI;
5. using UnityEngine.Networking;
6.  
7. public class ChatScript : NetworkBehaviour
8. {
9.  
10.     public GameObject ChatPanel;
11.     public GameObject TextObject;
12.     public InputField Input_Field;
13.     [SyncVar]public int maxMessage = 25;
14.     [SerializeField]
15.      List<Message> messagelist = new List<Message>();
16.  
17.  
18.     void Update()
19.     {
20.  
21.         Input_Field = GameObject.Find("InputField").GetComponent<InputField>();
22.         ChatPanel = GameObject.Find("ChatPanel");
23.         if (Input.GetKeyDown(KeyCode.Return))
24.         {
25.             if (Input_Field.text != "")
26.             {
27.                 if(isServer)
28.                 {
29.                 RpcSendMessageToChat(Input_Field.text);
30.                 Input_Field.text = "";
31.                 }
32.      
33.                 else
34.                 {
35.                     CmdEnviar(Input_Field.text);
36.                     Input_Field.text = "";
37.                 }
38.             }
39.         }
40.     }
41.  
42.     [Command]
43.  
44.     void CmdEnviar(string text)
45.     {
46.         RpcSendMessageToChat(Input_Field.text);
47.     }
48.  
49.     [ClientRpc]
50.     public void RpcSendMessageToChat(string text)
51.     {
52.         if(messagelist.Count >= maxMessage)
53.         {
54.             Destroy(messagelist[0].TextObject.gameObject);
55.             messagelist.Remove(messagelist[0]);
56.         }
57.         Message newMessage = new Message();
58.         newMessage.text = text;
59.         GameObject newText = Instantiate(TextObject, ChatPanel.transform);
60.         newMessage.TextObject = newText.GetComponent<Text>();
61.         newMessage.TextObject.text = newMessage.text;
62.         messagelist.Add(newMessage);
63.     }
64.  
65.  
66.     [System.Serializable]
67.  
68.         public class Message
69.         {
70.         [SyncVar]public string text;
71.         public Text TextObject;
72.         }
73.  
74.  
75. }

and for the full error code :
Trying to send command for object without authority.
UnityEngine.Networking.NetworkBehaviour:SendCommandInternal(NetworkWriter, Int32, String)
ChatScript:CallCmdEnviar(String)
ChatScript:Update() (at Assets/Script/ChatScript.cs:35)