Your add to cart working and redirecting to cart page (https://www.plantsbypost.co.uk/cart). You need to add cart drawer popup to help customer.
The functionality of add to cart needs to be checked and correct the code.
Also buy now button needs to be corrected.
Let me know if I can help you.
Yes I can surely help. Can you please email me now
My email is email@example.com
Also on Email I will explain you about buy now button that needs to be corrected.
Awaiting your email