How do I enable detailed error messages in the web.config?

Detailed Errors allows for debugging errors in your code.

Without detailed errors enabled, upon an error – the webserver will display a 500 Internal Server Error.

You are able to add the code below to your web.config file within the <system.webServer> </system.webServer> to enable detailed error :
<httpErrors errorMode="Detailed"/>

Here is an example:

<configuration>
   <system.webServer>
      <httpErrors errorMode="Detailed"/>
   </system.webServer>
</configuration>

The code sample above does not constitute a complete of your web.config file.
Please do not replace your existing web.config file with the code above & do a backup of your web.config file before changing.