For Steam users that are having issues with Steam Guard not showing Code, you can use the suggestions listed in this post to resolve the issue.

How to find your Steam Guard Recovery Code A lot of people are downloading Dota Underlords on their smartphones, and they are having to deal with Valve's Steam Guard Mobile Authenticator.

There's not a lot to the app itself, which is fine. All it needs to do is give you your Steam Guard codes and access to trading, a feature which also requires the extra authentication.

Let's be honest; if you regularly use Steam Guard, you probably use the mobile app, especially since the email alternative often leads to rummaging through your spam folder for a code.