Ignore the URL link, I couldnt leave it blank.
Check your email for the subject line "Your chance at a holiday surprise awaits" from Microsoft. Scroll down to and click the "See if you've won" button to add the $5 giftcard to your account. Im guessing everyone that gets the email is a winner, as is usual with these emails.
Edit: The mobile app is truly the worst, it changed the post title after adding the url. I have now updated it.