same issue here
https://support.openrainbow.com/hc/en-us/sections/201292944-Service-Notifications
Again Is the company and User linked to a pbx? in "communication" in the company settings Then the Rainbow will tell the PBX to make the Call for the User to ANY number you tell it
Ah but i think the outlook plugin needs subscription license but free you have to put number in rainbow
any number Once the rainbow company is linked to a PBX! And the user has a phone linked to account, even essential (free) has RCC (Remote Call Control) of Alcatel deskphone