New business account does not exist and cannot log in as does not have authorisation

Dear LH,

As a forum moderator, I am not able to inspect your subscription or tenant to diagnose and fix this directly. My role here is limited to general guidance you can apply from your side.

First, a Microsoft 365 Business subscription does not use a product key. Once the license is assigned to the business user, Office on your Mac activates simply by signing in with that work account.

Your personal Microsoft account and your new business account are two separate identities, so signing in with the personal one will report that the account does not exist. It is also possible the tenant has not finished provisioning yet, which produces the same message and usually clears within a few hours of purchase. To narrow it down, could you share a few details:

• Did you receive a welcome or confirmation email from Microsoft, and what address does it show?
• Which address are you signing in with, and where, at office.com, admin.microsoft.com or somewhere else?
• What is the exact wording of the error, including any code such as AADSTS50034?
• Did you complete the full setup wizard, including any domain step, or stop after payment?
• Did you buy directly from Microsoft or through a partner or reseller?
• Which Business plan did you purchase? Business Basic does not include the desktop apps.
• Does the same thing happen in a private browser window?

It is also worth checking whether the payment actually completed, since a purchase that failed at the final step can leave you with a confirmation email but no active tenant.

I'm looking forward to your reply.