Question: How do you troubleshoot IIS Asp.Net Core 3.1 that is running in Production Mode. Answer: If you want to troubleshoot an Asp.Net Core 3.1 running in IIS, you need to see the errors that the application is emitting by adding a Development environment variable in IIS. - Open up IIS - Click on "Configuration Editor" - Click in the Dropdown menu that says "Section" and choose "System.webServer" - Find "AspNetCore" and click on it. - Make sure the "From" Dropdown menu is populated by the "dashboard Web.config" - In the Main Window, Click to the right of "EnvironmentVariable" on the "three dots" - Click "Add" to add a Key-Value pair - In the "Name" textbox type in "ASPNETCORE_ENVIROMENT" and in the "Value" textbox type in "Development" After you fill in the textbox, close the window and test your application in IIS to see the error. [Important]: Make sure you reverse the settings to Production Environment Variable when you are done. Errors: If you find that you can't Edit the Environment Variables in the IIS to change to Production or Development follow the solution below: Step 1: Open notepad as an Administrator Step 2. Copy and paste %windir%system32inetsrvconfig path into Notepad Step 3: Change from *.txt to all Files to be able to see the config file and edite it. Step 4: Edit applicationHost.config file Step 5: Press (Ctr + F) to search in applicationHost.config file for ASPNET  Step 6: Change from true to false next to Lock-Section