Can't add subdomain on Azure Domain

Question

I'm trying to add the subdomain pk.alnasser.net to my account, and I'm getting an error "Failed to add domain Unknown". The root domain has been verified at the registrar and I was able to add another subdomain successfully eg.alnasser.net

Answer 1

IF you own both tenants, then you can delete the custom domain in the existing one, that would allow you to add it the new tenant. It may take awhile before it lets you however and there are some caveats:

https://learn.microsoft.com/en-us/azure/active-directory/enterprise-users/domains-manage#delete-a-custom-domain-name

If you can't get this to work, I would open a support case in your Azure tenant and ask for assistance.

Answer 2

Is pk.alnasser.net already verified in another tenant?
If I do a lookup of those domains, they are pointing to two different Tenant IDs

https://www.whatismytenantid.com/

Answer 3

The issue, I'm facing now that my old on-prem mailbox is not operational and I'm being asked to sign into account under that subdomain
"We can't add this domain to your account because other people have already signed up for ‎Microsoft 365‎ using an email address ending in ‎pk.alnasser.net‎."
which can not be possible, are there another way of confirming ownership/ transferring the domain to my current tenant?