Can't Change Apple ID. Get "You can only add the @icloud.com address that is already on file in your account."
So, I am trying to change my apple ID from an old third party email. I have an icloud.com alias already setup and use that for my email. However, I want to go ahead and leave the third party email behind. I also want to be able to use third party mail support. However, when I hit the button to change it I get the following message when I enter my icloud.com alias email address, " You can only add the @icloud.com address that is already on file in your account." What do I do to resolve this?
Regards, C.