Accessing API over IPSec VPN

[ninjamonkey198206]

Has anyone got this working?
I'm using this on my personal homelab router and my parents (they're, erm, ancient and need extra help staying safe online) and have a always on site to site IPSec VPN in place so I can easily troubleshoot issues with their LAN or Wi-Fi.
I also use Homepage to keep track of all my container apps and now my PFSense box, but I can't seem to get the API on my parents box to work (using the widget in Homepage).
I haven't spent a ton of time on it, as in this case it's only for convenience, just wondering if anyone had run into a similar situation and figured out how to get things playing nice.