Problems with built-in CODE server

I’m trying to configure nextcloud for a kind of convoluted setup and haven’t been able to find documentation for this exact scenario. If anyone knows of any or has experience with the issues involved and can can provide some pointers it’d be much appreciated.
The system is accessed through
Host name resolves to a router in front of a private network
Router forwards port to internal address
Host at runs nginx as a reverse proxy to lcx container
Container at runs apache2 with nextcloud in /var/www/html

Everything except built in Collabora seems to work fine.
settings/admin/overview give me a warning about the proxy but provides no details and all relevant config settings have been made
“The reverse proxy header configuration is incorrect, or you are accessing Nextcloud from a trusted proxy. If not, this is a security issue and can allow an attacker to spoof their IP address as visible to the Nextcloud. Further information can be found in the documentation :arrow_upper_right:
If there’s a way to get details of what exactly it’s seeing wrong that’d be nice. Other wise everything works.

settings/admin/richdocuments seemingly randomly can/can’t reach the built in CODE server. The interface on this page reacts erratically, saying a server is reachable when only half the URL has been completed, displaying all options ticked, etc. I really have no way of knowing the state the back end is in from it. If there’s a way to do this from a shell that’d be useful.

Depending on the mood it’s in clicking on “Files/Documents/Welcome to Nextcloud Hub.docx” will either download the file directly or attempt to open it with the built in CODE. When it feels like using the CODE it fails, apparently because it’s trying to use the internal IP
Blocked loading mixed active content “
All the overwrites listed in the documentation links from settings/admin/overview are set. Obviously I’m missing something that tells Collabora to use those. But I have no idea what it is.