mobile menu not working on iPhone/Safari

Hi guys, I’ve been struggling with your mobile menu. I have done some modifications as can be seen on the website. The problem is that it seems to be working flawlessly on Chrome while testing, on my Android phone, on any responsive tester found online.
But the customer keeps complaining that mobile menu is not working on his iPhone or his Safari when switched to mobile mode. He says X button is not working, the dropdown menu is not working, basically anything apart standard links and +/- buttons. Can you please do some testing on Apple devices and let me know what is wrong with my code? Thank you in advance.

The page I need help with: [log in to see the link]