@ashok hirpara ·,
The User principal name is a unique attribute that can not be changed for any account where source is other than Azure Active Directory . Your local directory is not authoritative for it . The Microsoft account system is the source of the account. this account is like a guest account which just has references for the same. In your case source is Microsoft Account which is a consumer LiveID system and is separate from Azure AD . When you sign up for azure or someone invites you to a azure subscription/directory , a guest reference account gets created which has its own limitations in the local directory and can not be changed. Please check B2B collaboration / guest accounts on https://learn.microsoft.com/en-us/azure/active-directory/b2b/user-properties
when you say the primary email has changed , if you mean that you have now added a new account then it should not be added there. Try logging in to https://account.microsoft.com with your Microsoft Account or the account you have changed to . The account you will be able to use to logon here tells us that its a MSA (Microsoft Account) .
If you mean that account earlier was anon@USER and now you have changed it to anon@USER and you have signed up from both emails as a Microsoft Account then you will need to add the new account again by inviting the user as a guest user and providing the owner rights on the subscription object and providing it global administrator role in the Azure AD . And that will be a separate account . You wont be able to update the Email address on this account because it is by design and your azure AD instance is not authoritative to change that attribute within Azure AD by design.
If this does not help you , please provide more details about what you mean by primary user . I believe you can just invite the new account using IAM blade as shown in the linked articles as they have steps with screenshots and are easy to follow. I think that will solve your problems. Please go through the articles and I am sure you will be able to figure it out . If you still have questions though , please let us know and we will be happy to help.
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