Can't check websocket message in alb idle timeout?

As described in this document, the ALB idle timeout is 60 seconds by default.
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/application-load-balancers.html#connection-idle-timeout

By default, Elastic Load Balancing sets the idle timeout value for your load balancer to 60 seconds. Use the following procedure to set a different idle timeout value.

Therefore, if the timeout is shorter than the WebSocket message transmission, the ALB idle timeout value must be increased or the communication will be disconnected.
Try it for 300 seconds and see if the error goes away.