How to configure client to connect on different port?

I’m trying to set up urbackup via an reverse nginx proxy, in the configuration of urbackup, my reverse proxy translates to the dockerized instance on 55415 for the remote clients, the settings under settings -> internet get pushed out to clients, so I cannot specify 443 here as I have other services running on that port (my nginx proxy).

Is there a solution to this?

I am trying to accomplish a similar issue but using httpd with reverse proxy to:
ProxyPass / http://localserverip:55414/ (This is for the web gui which is fine this way and uses httpd as the ssl pass off)

Internet clients however show connected at 443 but the proxy:
ProxyPass / http://localserverip:55415/
Never sees the connection or internet client.

Trying to get some incite on this please.

Centos Proxy server (httpd) and urbackupsrv runs on another box with seperate local ip (ubuntu server 20 Os)