this one way

when a call comes if there is no agent in loggedin state an email will be sent to the supervisor

the can be done by adding get reporting statistics before the cal go to the queue and then make if step

check if the number of logged in agents = 0 then send eamil if no normal

if you want go to advenced level you may use trigger application and then you run another script that call the supervisor number and play a prompt one no agent loggedin !

good luck

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