SFTP from UCM IPBX to NAS not connecting

We have two locations.
Location 1: has Tailscale running on Raspberry. One machine is a UCM IPBX that needs connection to the NAS in location 2
Location 2: has also Tailscale on Raspberry and also on Synology NAS
But I cannot reach the NAS over SFTP from the UCM.
Thanks for pointers

I suspect that the --snat-subnet-routes option will be useful. It will allow the subnet on each end to see the IP addresses from the subnet at the other end.

Thanks. I tried to set the subnet-routes-false, but that did not solve the problem and it also created all kind of other issues.

I got a solution from support:
Add static route in IPBX UCM: 192.168.XXX.YYY to where XXX.YYY is the private IP address of the RaspBerry Pi hosting Trailscale.
They also suggested I might have to disable the snat on the source, but so far it works without that setting.