Pop Up Pro not showing on Safari mac

Hi,
Pop Up pro isn't showing the pop up on Safari. I tested it on many other browser where it works fine. Safari is being stubborn for some reason. And since I am serving an ad in the pop up - it is effecting my metrics to the ad buyer - I'm losing ad impressions!

Safari Version 9.0.3 (10601.4.4)

Any ideas as to why it is not working?