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Could you please verify that the MPN account you are using for publisher verification is the partner global account (PGA) for your organization. Location MPN IDs are not supported for publisher verification.
Verify that the domain of the email address used during MPN account verification matches the publisher domain configured on the app or a DNS-verified custom domain added to the Azure AD tenant.
Go to the MPN tenant management page Ensure that the Entra ID tenant where the app is registered is on the list.
If it is not, you will need to add it. Please be aware that this will allow Global admins of that tenant to be admins of your MPN account- you should only proceed if you are ok with that.
Also, could you please double check the steps you have followed. if the issue still persists, please help me with the steps you have followed and screenshots.