Hi everyone, I've been trying to get to the bottom of this for some time. But I think that I'm getting somewhere now.
Some customers are randomly getting Cart and Payment Errors. Sometimes it won't give an option to pay and other times they'll make it as far as Paypal before not being able to pay.
The logs are saying "Frontcontroller::init - Cart cannot be loaded or an order has already been placed using this cart"
Having just spoken with a customer who was having this problem, I traced the Object ID through the "Active Shopping Carts" section. I found that the cart number is associated with an order placed when using Prestashop 1.6 back in 2022. The on screen product differs to the one placed in 2022 and the customer associated with the 2022 order hasn't logged in since then.
I paid someone to help with updating to 1.7 and they transferred all the old customers and orders into the new 1.7 shop. I believe that when some new customers put something in a Cart, that cart is being assigned a number used previously on the 1.6 shop.
Another interesting point is that the customer can overcome the problem by switching to Incognito mode in their browser.
Having lived with this problem for nearly a year, it makes me feel sick to wonder how much business we've lost because of it.
I suppose that my question is, what is the easiest way to fix this please?