SocketIOEvent could not be found

Im using fpanettieri/unity-socket.io to connect and send data to/from a node server. I have the connections to the server working but I cant get the data back to unity from the node server. In my update I use:

 socket.On ("position", TestMsg);

This calls:

  public void TestMsg(SocketIOEvent e)
         {
             Debug.Log(e.data);
         }

But before the project even starts i get an error saying:

Assets/SocketResponder.cs(27,29): error CS0246: The type or namespace name `SocketIOEvent' could not be found. Are you missing a using directive or an assembly reference?

Even though i have the dll's provided by the git repository in my project which contain SocketIOEvent. On the server side i use this which has been tested on a website so i know it works:

 io.on('connection', function(socket)
 {
     console.log("connected");
     socket.on('beep', function(msg)
     {
         console.log(msg);
         socket.emit('position', msg);
     });
 });

Is there any reason or is this a pro only option?