Where do I sign up for Google Ad Manager?

Your Ad Manager account is permanently linked to your Google AdSense account. If you have more than one Google AdSense account, make sure you sign up for Ad Manager using the right one. Visit admanager.google.com to sign up for an account. Click Create account, then choose For myself or To manage my business.
For More Information Please Refer:
https://support.google.com/admanager/answer/7084151?hl=en
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