WebSocket: Accept client connection
First of all you should handle TElHTTPSServer.OnBeforeWebSocketServerUsed() event, which will be fired when a client initiates WebSockets connection. In the parameter of this event your code will receive an instance of TElWebSocketServer. This instance is used to work with this client via web-socket connection. The instance should be configured by your code before usage. In particular, it's necessary to assign event handlers to TElWebSocketServer.OnBinaryData and/or TElWebSocketServer.OnTextData events.
TElHTTPSServer.OnWebSocketConnectionEstablished event is fired when incoming WebSocket connection is already established. After that you can send and receive data via the newly established connection.