Change Shared Booking Page (URL) UPN/SMTP to non-default Tenant Domain URL

Sometimes it might be desired to modify the Shared Bookings-Page URL in terms of using a different UPN/SMTP in the URL.

By default setting up a shared booking page it uses (as long as it's free) the page name + default Tenant domain to build the url, like a page called "my TestPage" might result into mytestpage@default-domain.com, e.g. https://outlook.office365.com/owa/calendar/mytestpage@default-domain.com/bookings/.

Now we have several companies covered by the same tenant within our holding, and it might be a better approach to have a page like https://outlook.office365.com/owa/calendar/mytestpage@**custom-domain.com/**bookings/ or even https://outlook.office365.com/owa/calendar/**different-name@custom-domain.com**/bookings/

There are a few posts online, but somehow none reliable really leads me to success. I managed it once to get my address changed (entirely - including sharing link), but honestly I don't know which peace from all what I've done was the key to success. And from there I get my desired URL to make it work by changing the UPN/SMTPAddress to what I need, but it never becomes also the official URL I see under https://book.ms for this page. Like now https://outlook.office365.com/owa/calendar/mytestpage@custom-domain.com/bookings/ also works after a few minutes, but the initial https://outlook.office365.com/owa/calendar/mytestpage@default-domain.com/bookings/ keeps being official and my change only works due to some redirection made behind the scene when I change UPN in Azure or O365 Admin.

I basically followed this page https://blog.markdepalma.com/?p=681 - but the only one shared booking page I managed to get modified official url I did it by my intuition.

I also had this https://www.exchangemaster.ch/faq-000178-how-to-change-the-sender-and-reply-e-mail-addresses-in-microsoft-bookings/# - but somehow that makes no sense because I only can run this command successfully if I use the already assigned UPN), which from what I was told is in the same time also the smtp address of this mailbox/calendar), otherwise it says "WARNING: Proxy address "different-name@custom-domain.com" is used as WindowsLiveId. So it can't be removed from list of email addresses. To remove it, first change the WindowsLiveId.". If I change the Windows LiveID, which I consider being UPN, it implicitely changes the smtp address anyway too, though.

And I also have to mention, running "Get-mailbox -RecipientTypeDetails SchedulingMailbox | Select-Object DisplayName, Alias, PrimarySMTPAddress" shows me the expected PrimarySMTPAddress, just the official URL provided to share does never reflect this.

Hope someone can give me a hint, how I can get the official sharing url for a shared booking page to become modified too.

kind regards,

Dieter