I think I am having the same problem.
I used the developers own contact form:
https://www.patsatech.com/contact-us
I wrote:
I have installed sagepay-server-gateway-for-woocommerce and I am finding that my transactions are being reported as invalid.
I called up SagePay and they told me that the shop is returning invalid. I don’t see any error massages and everything look fine, e.g., I go to the shop, I add a product, I go to the checkout, I click place order, I get on the sagepay and enter my card detail, I confirm the details and click button to move on and then I am back at the shop.
It almost looks like it worked, I see no errors, I am back on the shop website, but I see no order confirmation and my basket/cart still has the item(s) in it and there are no order confirmation emails.
When I got to MySagePay admin and look at this transaction I see this message:
Transaction completed but Vendor systems returned INVALID or ERROR in response to notification POST. Transaction CANCELLED by the Vendor.
SagePay told me the order was ok, everything passed its checks and then sagepay tried to return to the website and confirm everything was OK but this is when our shop return Invalid code, this terminates the transaction.
Do you have a solution for this problem?
