Hello,
Try to clear browser cache and check one more time.
I’ve checked your site in Chrome – http://prntscr.com/q19q85 and Safari – http://prntscr.com/q19r1q
In which exactly browsers do you have the problem with adding to cart?
Please provide screenshots of the problem with the paying.
You can use Lightshot Screenshot tool https://app.prntscr.com/en/index.html and provide the link to the screenshot here.
Regards