I have a room resource room@domainA.com defined. This rooms resource should be accessible from several Microsoft 365 tenants. Therefore I have set up sharing in the Exchange admin center for both domainA and DomainB allowing them to share free/busy information.
From domainA where the resource is defined I have full functionality. I can use room finder, I can add it as a shared calendar and view the full calendar. However from domainB I cannot add it as a shared calendar or use room finder.
It is possible to create a meeting in domainB and add the domainA resource as a participant. Then I get the schedule assistant to show free busy status and the room also auto replies with an accept of the invite. This indicates that the calendar is shared cross tenants.
I can not understand why I am not able to add it as a shared calendar? I use outlook and choose open shared calendar but get the error message shown in the image. attached.