A domain-linked email (DLE) is an email address associated with your website URL. To ensure compliance with state and federal ad authorization requirements, you MUST register with an email that matches the URL domain for your entity. In short, it ensures that the person setting up the account to run ads on behalf of a campaign, organization or agency is who they say they are...and actually affiliated with the entity.
Sorry, a personal email—such as those from Gmail, Yahoo or others—is not acceptable when registering for a new Ads Platform account.
Most domain registrars offer free or discounted domain-linked emails as part of your domain purchase. You can alternatively set up a domain-linked email address with Google Workspace or Microsoft Outlook (amongst many others) for a nominal fee.