How to set web.config file to show full error message (.net core 2.1)

web.config

<system.webServer>
    <httpErrors errorMode="Detailed" />
    <aspNetCore processPath="dotnet">
        <environmentVariables>
            <environmentVariable name="ASPNETCORE_DETAILEDERRORS" value="true" />
        </environmentVariables>
    </aspNetCore>
</system.webServer>

You can configure it in your Startup.cs file. By default, it shows the Developer Exception Page only in development mode:

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}
else
{
    app.UseExceptionHandler("/Home/Error");
}

If you replace this part just with app.UseDeveloperExceptionPage(); it will always show the detailed error message.

You can read more about it here: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/error-handling?view=aspnetcore-2.1

For me, enabling ASPNETCORE_DETAILEDERRORS didn't do anything, but changing ASPNETCORE_ENVIRONMENT worked:

<environmentVariables>
  <environmentVariable name="ASPNETCORE_ENVIRONMENT" value="Development" />
</environmentVariables>

More info: https://docs.microsoft.com/en-us/aspnet/core/test/troubleshoot-azure-iis?view=aspnetcore-3.1#enable-the-developer-exception-page