If you want to connect HXA.io with your Microsoft Exchange EWS Endpoint by using a Service Account to read all Room Mailboxes you have to setup a Room List (Distribution Group from Type RoomList) via Exchange Shell.
New-DistributionGroup -Name RoomList01 -DisplayName "Building 1 Conference Rooms" –PrimarySmtpAddress email@example.com –RoomList -ManagedBy firstname.lastname@example.org
After you create the RoomList you have to add the Rooms to the list.
Add-DistributionGroupMember –Identity Room01 -Member email@example.com
If you want to check the configuration of your RoomList you can use
Get-DistributionGroup -Identity Room01 | FL
If you need further information please check the Microsoft Docs https://docs.microsoft.com/de-de/powershell/module/exchange/get-distributiongroup?view=exchange-ps