Zulu Default Phone app in Windows 10

I am running into a weird issue with the paid Zulu module Outlook add-in for our installation. Whenever we try to dial a number from within an email we get the following popup.

It seems like Windows is not recognizing that Zulu is supposed to be the default phone app and I am not sure how to force it to be.

I tried looking around in the Default programs section of Windows 10 Settings but am unable to figure out what setting is not set to enable dialing from Outlook email.

Any assistance would be greatly appreciated.

This is fixed in the beta version of Zulu