socketChat | A real-time messaging application built using Socket.IO | Socket library

I'm trying to create a project and one of its functionalities is having a chat. The structure for chat is: App made in React Native and the backend i'm using Flask. For the backend i have many different routes and my intention is to create another route for handling user messages with WebSocket. I'm having many issues with flask_socketio. I tried a small version of websocket using NodeJs and it worked flawlessly. That's what i did so far:

I need an app to connect a board by Wifi. There are four fragments that by clicking everyone I have to write arraybyte or one byte and then read arrayByte. At first time, I just read arrayBte without writing and it is work perfect, but by clicking other fragments, I always get null. This is my code:

I am creating an chat application using socket.io, every things going perfect but when I am handling user typing notification I am getting error like below

Error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[SocketChat.ChatViewController handleUserTypingNotification:]: unrecognized selector sent to instance 0x7f817653d710

and now I will show you my code for better expiation

Code:

Update onMessageReceived called in API 19 but not on 23 and 24. Update

I am sending FCM notifications from a server, I can receive notifications but onMessageReceived is not called(foreground, background), even with data messages. This is the code I'm using.