Accessing a master module via VPN

Hi

I have a remote machine that has a teltonika modem on it that I can access remotely using OpenVPN. I know the configuration of the VPN is good because I can access the Teltonika admin pages (192.168.10.1) without issue from my laptop connected to my phone hotspot on 192.168.111.100

In the Teltonika  admin pages I can see that the modem has allocated a DHCP address to the MD4-10 module and I can ping it and successfully get responses from the display.

In Design I can see the MD4-10 module in the discovered modules but its discovered with an IP address of 172.16.0.1 which is the VPN endpoint assigned to the openVPN tunnel at the modem end. Ive added a static module with the right IP address of 192.168.10.14, but unlike the discovered module the indicator light never turns green.

Any attempt to communicate with the module fails with a "failed to open a new communication session" error.

Has anyone dealt with this issue before and sorted a way through it, I'm trying to work out if this behaviour is due to a missconfiguration of my vpn, or if its by design because I know Parker have a solution exactly in this space. If my understanding is correct though its a 3G based solution where Australian Telco's have all announced end of life for 3G in comming nearterm months so not a particularly long life solution.....

help if you can