Can I backup Synology NAS to offsite Synology Router using WebDAV over VPN

I have a sinology router, RT2600ac which is hosting an IPSec VPN and WebDAV with a USB connected disk.

My goal is to have my Synology Diskstation (which is a NAS) at another location connect to the Synology RT2600ac router’s VPN and then run hyper backup using WebDAV to access to USB connected disk.

I am able to connect to the VPN but I can’t get hyper backup to connect to the WebDAV server.

Is what I’m proposing even possible? Specifically to use a VPN to connect to WebDAV to securely backup files?