Not able to add an alias email in microsoft 365

[jopapa777]

When I go to add an alias I get this error.
An Azure Active Directory call was made to keep object in sync between Azure Active Directory and Exchange Online. However, it failed. Detailed error message: Another object with the same value for property proxyAddresses already exists. DualWrite (Graph) RequestId: 350faf2a-03ff-4a45-8e45-dc127bcce2b1 The issue may be transient and please retry a couple of minutes later. If issue persists, please see exception members for more information.

Any help would work.

[#2]

You seem to already have an object that uses said email. Easiest way to located the object is via:

Get-Recipient address@domain.com

[#3]

Where do I do the Get-Recipient? I tried adding aliases for other accounts/email addresses.
Using both m365 admin console, and Exchange admin console...

[#4]

Connect to Exchange Online PowerShell: https://docs.microsoft.com/en-us/powershell/exchange/connect-to-exchange-online-powershell?view=exch...

[#5]

Thanks Vasil,
But since I can add alias to group email addresses, but just not to individual email addresses.