If a recipient can't be found for a private message sent by a client, the server sends the "player not found" error message to the client

Subsurface/Source/Networking/GameServer.cs

@@ -1451,8 +1451,25 @@ namespace Barotrauma.Networking
                                     (c.Character != null && command == c.Character.Name.ToLowerInvariant()));
 
                                 if (targetClient == null)
+                                {
+                                    if (senderClient != null)
+                                    {
+                                        var chatMsg = ChatMessage.Create(
+                                            "", "Player \"" + command + "\" not found!",
+                                            ChatMessageType.Error, null);
+
+                                        chatMsg.NetStateID = senderClient.chatMsgQueue.Count > 0 ?
+                                            (ushort)(senderClient.chatMsgQueue.Last().NetStateID + 1) :
+                                            (ushort)(senderClient.lastRecvChatMsgID + 1);
+
+                                        senderClient.chatMsgQueue.Add(chatMsg);
+                                        senderClient.lastChatMsgQueueID = chatMsg.NetStateID;
+                                    }
+                                    else
                                     {
                                         AddChatMessage("Player \"" + command + "\" not found!", ChatMessageType.Error);
+                                    }
+
                                     return;
                                 }
                             }