Hi

Yeah i found this confusing when i first looked at it too.

The config isn't transformed at build time but rather run time, and depends on the runtime state that the site is in.

This is actually determined by the value of the ASPNETCORE_ENVIRONMENT environmental variable. the file merged into the appsettings.json takes the form appsettings.{{environment}}.json. eg. appsettings.development.json.

See https://docs.microsoft.com/en-us/aspnet/core/fundamentals/environments?view=aspnetcore-6.0

when you are working locally, there is usually a properties/launchsettings.json file that sets this up so you will see something like :

  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },
    "Umbraco.Web.UI": {
      "commandName": "Project",
      "dotnetRunMessages": true,
      "launchBrowser": true,
      "applicationUrl": "https://localhost:44328;http://localhost:17621",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }      
    }

When running on something like azure or a local iis server this needs to be set to 'production' or 'release' or what ever it is you want to use for your appsettings file.

For example for azure web app there you can set it in the portal : this blog post has a good summary of the options https://thecodeblogger.com/2021/04/12/multiple-ways-to-set-hosting-environment-in-net-applications/