Can't start mattermost in docker: config.is_valid.site_url.app_error

Mattermost in docker hates my development site url, and it’s probably something simple. Can someone please help?

I have provided Perfectly valid SiteUrl argument similar to (“https://chat.private-development-server.ca/”)
The app is running as root within the docker container
The container is behind a reverse proxy providing https termination and is accessible from the internet
I have even tested the go parsing of this, and I have zero idea why it does not work.
here is the first few lines of my config

{
    "ServiceSettings": {
        "SiteURL": "https://chat.private-development-server.ca/",
        "WebsocketURL": "",
        "LicenseFileLocation": "",
        "ListenAddress": ":80",
        "ConnectionSecurity": "",
        "TLSCertFile": "",
        "TLSKeyFile": "",
        "TLSMinVer": "1.2",

And the full error looks like this:

chat.eagle-research-mail.ca | Using existing config file /mattermost/config/config.json
chat.eagle-research-mail.ca | Starting mattermost
chat.eagle-research-mail.ca | Error: failed to load configuration: failed to create store: unable to load on store creation: invalid config: Config.IsValid: model.config.is_valid.site_url.app_error,