Websockets "invalid frame header" error Flask-Socket IO

Question

I am using flask-socketio and everything works awesome but when sending one value using emit, the chrome developer tools is showing error BUT EVERYTHING IS WORKING AS EXPECTED.

"WebSocket connection to 'ws://127.0.0.1:5000/socket.io/?EIO=3&transport=websocket&sid=240eada2f8bb4ce889ae90ffbf9cb6ea' failed: Invalid frame header"

Sending a value of input field is working fine but what I want to send is a substring of an input value. Have checked the type of the substring and it is string.

javascript :

           value1=$('#input_box').val();

           var term = value1.substr(value1.lastIndexOf("!") + 1);

           socket.emit('qqq event',{data:term});

flask:

          @socketio.on('qqq event', namespace='/test')

          def my_event(term):

                 term=term['data']

                 emit('xyz',{'data':term})

With this code, the value is being sent to flask server but chrome shows error. As mentioned, Everything works but just curious to know the reason for error.

When I change the value to the value of the input field, error is not shown.