Cannot connect Docserver to external PostgreSQL DB over LAN

I have a ProxMox homeserver running multiple containers:

Nextcloud = 102 = 192.168.2.63
OnlyOffice = 104 = 192.168.2.65
PostgreSQL = 105 = 192.168.2.66

All containers are unprivileged Debian12 stable images.

Nextcloud and OnlyOffice are correctly configured and successfully web-facing.

Currently OnlyOffice is using the PostgreSQL db installed with the AIO script within the same CT but I am migrating all services to the dedicated PostgreSQL CT 105, and herein lies my problem - no matter what I try, I cannot point the docserver to my Postgres CT.

I have created the user, database and password within Postgres and tested connection from OnlyOffice with:

psql -h 192.168.2.66 -U onlyoffice -d onlyoffice

which successfully connects to the database, as checked with:

SELECT datname, usename, client_addr, client_port, state
FROM pg_stat_activity
WHERE client_addr IS NOT NULL;

which returns:

datname | usename | client_addr | client_port | state
----------------±---------------±-------------------±--------------±------
onlyoffice | onlyoffice | 192.168.2.65 | 51232 | idle
(1 row)

sql block in local.json:

   "sql": {
    "type": "postgres",
    "dbHost": "192.168.2.66",
    "dbPort": "5432",
    "dbName": "onlyoffice",
    "dbUser": "onlyoffice",
    "dbPass": "REDACTED"
  },

I even attempted to pass environment variables before running the install:

export POSTGRESQL_SERVER_HOST=192.168.2.66
export POSTGRESQL_SERVER_PORT=5432
export POSTGRESQL_SERVER_DB_NAME=onlyoffice
export POSTGRESQL_SERVER_USER=onlyoffice
export POSTGRESQL_SERVER_PASS=REDACTED

This had zero effect and the default arguments were passed upon installation.

I cannot find documentation on this specific issue or bug ANYWHERE, so if anyone could help that would be amazing, as at the moment it’s looking like I might have to spin up a docker container to force the variables to pass, which I really don’t want to do on this install!