This impacts any person or company who is creating a Google Ad Manager account for the first time. If you don’t have a Google Ad Manager account, but you do have an AdSense or AdMob account that has already been verified, you should not have to complete verification. You should confirm this within your Google Ad Manager account by navigating to your 'Payments' page. For more details, click here.
Who will be required to complete GAM’s identity and address verification?
Linley