Prerequities:
The service account is created. If not, check the article on how to create a service account.
Log in to your admin account and go to the Exchange admin center at https://outlook.office365.com/ecp/, then go to the Recipients → Resources section.
For each room used in MeetingRoomApp, set the permission to Full Access for the service user. Select a room and click on Edit. Go to the Mailbox delegation section and scroll down to the bottom of the window content where you can find the Full Access section.
Click on + and enter the service user’s e-mail address.
Select it from the list, click on Add → and then on OK.
