Navigate to Zone > Interfaces > Network.
In order to add a new zone, click Add.
Choose the kind of zone you wish to create and enter a name for it.
To save the zone, click OK.

Make sure the SSLVPN interface is positioned in the correct zone within your NGAF configuration, enabling traffic to be correctly processed and access the intended resources. Additionally, make sure the firewall rules are set up correctly for SSLVPN traffic and that the WAN IP has been added by double-checking the resource group settings.

Navigate to Policies > Firewall > Access Control.
To add a new firewall rule, click Add.
Choose the source and destination zones and give the rule a name.
Choose the rule's protocol and port number.
When the rule matches, decide what to do.
To save the rule, click OK.

If you don't sure the work around, please get help to the Sangfor Technical Team.

You can only assign Zones at the interfaces.

Click Create New > Zone after selecting Network > Interfaces.
Enter the zone's name, such zone_sslvpn_and_port4.
Include SSL and port 4. root to the members of the Interface.

The documentation of this can be seen at the KB and also you can contact Sangfor Technical Support

Are you all robots?  Or have you guys set up the NGAF before?

Sangfor TAC even tells me that is not supported to assign a Zone to the SSLVPN interface

Kindly be informed that the current version 8.0.47 does not support assigning a Zone to the SSLVPN interface.