Press enter to start typing and send message

Right now I have it so you have to click in textbox then type your message and click send button to send the message.

I want it so I can press the enter key then start typing and then press enter to send the messege. How could I achieve it?

 if(menuSrc.viewChat){
                 GUI.BeginGroup(chatRect, "");    
             
                 GUI.Box(new Rect(0,0,chatPanelSizeX, chatPanelSizeY), "");        
                 sizeY=margin;
                 GUI.Box(new Rect(margin,sizeY,chatBoxSizeX, chatBoxSizeY), "");                
                 chatScroll = GUI.BeginScrollView (new Rect (margin,sizeY,chatBoxSizeX,chatBoxSizeY), chatScroll, new Rect(0,0, chatBoxSizeX-margin*4, 20*menuSrc.networkSrc.chatContent.Count+margin*2));                        
                 for(int i = 0; i < menuSrc.networkSrc.chatContent.Count; i++){
                     GUI.Label(new Rect(margin*2,sizeY,chatBoxSizeX-margin*2, 30), menuSrc.networkSrc.chatContent[i]);
                     sizeY+=20;
                 }
                                     
                 GUI.EndScrollView();
                     
                 textChat=GUI.TextField(new Rect(margin, chatPanelSizeY-margin-chatFieldSieY, chatFieldSizeX, chatFieldSieY), textChat); // messege bar
                 if(GUI.Button(new Rect(chatFieldSizeX+margin*2, chatPanelSizeY-margin-chatFieldSieY, chatButtonSizeX, chatButtonsSizeY), menuSrc.text.gmChatButtonTxt) || Input.GetKeyUp(KeyCode.Return)){
 
                     if(textChat != "") {
                         string message = menuSrc.networkSrc.playerDataSrc.nameInGame+" : "+textChat; // name : messege
                         int maxChar = (int)Math.Round((chatBoxSizeX-20) / 6.8f);
                         if(message.Length > maxChar){
                             message = message.Substring(0, maxChar);
                         }
                         ChatMessage(message);
                         textChat = "";
                     }
                 }
                 GUI.EndGroup();    
             }                
         }
         
     }        
     private void ChatMessage(string message){
         menuSrc.networkSrc.SendChatMessage(message);        
     }
 }