Mobile Safari exclusive, JavaScript Error?

Question

I am in the early stages of a client site (hence blacked out info) and have run into a small issue. I have been using Opera's responsive screen sizing for mobile-first development. However, a good few hours in and I've finally connected using my iPhone 11 and the whole site has a big white border and limited JS functionality.

It appears that I have a JS error, but I can't access the console on mobile and Apple no longer offer Safari for Windows so I can't test it on my PC either.

Screenshots: Desktop Screenshot (Working):

Mobile Screenshot (Not working):

My question is, is it painfully obvious to anyone what I've done?

Any help appreciated. Thank you in advance.

Answer 1

Fixed: Using "//" instead of "https://" on my Bootstrap CSS & JS was the cause. Put back to "https://" and the page loads fine.