Problem with Mobile Responsive menu on Iphone

Problem with the Mobile Responsive menu on Iphone only. It works on the computer, Mac and android fine but not iphone. What could be the cause of this and what can I do to fix this. The website is: Please help this has me going crazy

thefrequentflyerfiles.com

Hi,

In the url provided you are not using our theme, we could not help you, speak with the support from that theme.

Thank you,

Cristian