On Call Roster User Calling

Hi All,

I currently have an alarm notification sending a voice notification to an on call roster made up of 2 users.

The way it currently works is that it makes the call to the first user and whether it is "answered" or "not answered" it then proceeds to call the next user in the roster.

What I'm trying to achieve is that it makes the call to the first user:

-If the call is answered then DO NOT call the next user.
-If the call is unanswered then call the next user in order of the roster.

Can someone please advise what is the best way to achieve this?

TIA