Gateway - PBI Services Connection Issue

Hi,

I have a private redshift cluster and I want to connect it with semantic models on pbi services. For the connecting semantic model on pbi services to redshift cluster I have configured an aws ec2 instance in the same vpc in which redshift cluister resides and I have configured pbi data gateway on it. I am able to query redshift db table using commands in cmd of that ec2 instance. pbi gateway is visible in pbi services and its status is online
Problem which I am facing is that when i create a new connection under that gateway using endpoint of redshift cluster, connection becomes visible in list of connections and shows status of online but it doesnot become available to choose in the list of connections to map uder gateway connections setting of any semantic model even after waiting for more than 1-2 days so i am unable to connect to redshift cluster using gateway and enpoint of redshift cluster but when i create a connection under that same gateway using enpoint of network load balancer, it gets created and becomes available to choose in the gateway connection settings.
I have checked all settings of ec2 instance esp security group and others and they all seem fine.
Please let me know how to solve this issue so that i can connect to redshift cluster through pbi gateway in pbi services using redshift endpoint otherwise configuring gateway in the vpc of redshift cluster seems useless exercise.

Let me know you need some other info