In the Administration Console, click Access Gateways > Edit > [Name of Reverse Proxy] > [Name of Proxy Service] > Web Servers.

Add all the SSL VPN servers that are part of the failover group as origin Web servers to the proxy service that you have defined.

Click TCP Connect Options.

Select Round Robin in the Policy for Multiple Destination IP Addresses field.

Select Enable Persistent Connections.

Save your changes and update the Access Gateway.