Please check the following:
1. Are the instances to place behind the load balancer already running (step 1 of the manual)? Is the port 8081 accessible on every instance?
2. Is the load balancer security group created and configured (step 2.4 of the manual)?
3. Are the listener target groups created (step 3 of the manual) and configured (step 2.5 of the manual)? Note that the example shows only how to create websocket listener (ports 8080 and 8443).