Emails to alias undeliverable. Bounced back as “mailbox unavailable” after changing primary alias.

I have an Outlook.com account that I've had for a while. I recently changed my account's primary email address from one address, to a recently created alias. For example:

Now, all my emails to *** Email address is removed for privacy *** are failing!! I'm not receiving any email on this account.

I've tested sending email to my other aliases, and they work fine. Emails to my primary email address also work. However this *** Email address is removed for privacy *** does not work.

Emails sent to this address are bounced back saying:

"Undeliverable"

"550 Requested action not taken: mailbox unavailable "

Please advise on what steps can be taken to get this email alias active again. This is critical as I've used this email address for many important accounts!

Thank you for your help! I really appreciate it.

-RC