I am the admin holder but I don't see an admin centre ?

Hello, @Craig Richards,

Welcome to the Microsoft Q&A platform!

Based on your description, I understand that you cannot add more domain emails to your account because you cannot see the admin center after using Microsoft 365.

What version of Microsoft 365 subscription are you using? Admin center is a management platform designed for enterprise and business users, so it is not available to users of personal subscriptions. If you have a personal subscription and need to add more users or manage multiple domains, you may need to upgrade to a business plan. You can choose the right plan by visiting Microsoft 365 for Business | Small Business | Microsoft 365.

If you have a business subscription, you should be able to go to https://admin.microsoft.com and log in with your administrator credentials to access the admin center. Moreover, if you think you should have administrator access, but actually don't, please check to see if any emails from Microsoft may have been sent to your spam folder. If you are still unable to access the admin center, it may be due to a setup issue or insufficient permissions. You may need to check that your account has the necessary administrator permissions.

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Thank you for your support and understanding.

Best Wishes,

Alex Zhang