LAN-only without SSL mattermost setup causing CORS errors

Troubleshooting
3

First, thanks a lot for the quick answer!
Yes, as this environment variable:

is passed in the compose (attached, the environment variables of the mattermost service):

    environment:
      # timezone inside container
      - TZ

      # necessary Mattermost options/variables (see env.example)
      - MM_SQLSETTINGS_DRIVERNAME
      - MM_SQLSETTINGS_DATASOURCE

      # necessary for bleve
      - MM_BLEVESETTINGS_INDEXDIR

      # additional settings
      - MM_SERVICESETTINGS_SITEURL

I have two questions:

  1. What would be the implications of setting AllowCORS From?
  2. Can it be due to the fact that I am not deploying the version with SSL?