In order to get Accredited you need to have at least 3 tagged videos in the last 30 days, as you mention in your post.
However, as World War Z cannot be found my guess is that is not on Keymailer's list of games, and cannot be tagged, thus making it "invalid".
I suggest you make a video of any other game that you have and has a Keymailer page with its own tag.
And even after meeting all the requirements accreditation can take a while to verify, especially if you don't have many subscribers.