To find out why your Ad Manager account can't be activated, either sign in to Google Ad Manager or read the email we sent you. The main reasons why we can't activate an account are described below.
We've found a violation with the Partner Guidelines
Review the Ad Manager Partner Guidelines to make sure you are following each guideline. If you’re able to fix the issues on your site or application then you may resume the activation process.
After you've adjusted your content, sign in to Ad Manager and confirm that you've resolved the issues. We'll then proceed with activating your Ad Manager account.
You have an existing Ad Manager account
Ad Manager policies only allow one account per publisher.
Publishers whose accounts have been terminated for invalid traffic or policy violations will not be allowed to open a new Ad Manager account as per the Publisher Policies.