Hello,
We are trying to make the order but always face out of stock error for a lot of products https://recordit.co/I73jyIGlOq . And that’s happens not just with our theme but also with the Storefront theme, we checked. Could you, please, solve the issue with the stock and then reply back. Also, I see that you have custom code in the XStore child theme. Remove that code and try to proceed to checkout. Do you still have the issue with the checkout without that code?
Regards