DNAT Problem

Hello.
I am trying to install a Rustdesk server in our office LAN. All works perfectly if I configure clients tu use private IP of the server (10.0.0.248); now I want to configure a DNAT in Sophos XGS using a secondary public IP address at our disposal.

1. I created a WAN Alias for the secondary public IP
2. I created an host for the Rustdesk server (RustSRV)
3. I created a service for the ports used by the Rustdesk Server: TCP 21115-21119 and UDP 21116
4. I created the DNAT rule that I attached, using the wizard.
5. I set the public IP of the Rustdesk Server on the clients, instead of the server private ip.

The PCs in the office LAN are unable to connect, giving an error on port 21116; however, if both PCs are outside the office, they work correctly.

What I'm going wrong?

In the DNAT rule summary, the outbound traffic from the internal server RustSRV uses the Primary IP address instead of the secondary one. Could this be the problem? Where can I change it?

Thanks for the support!