It's possible that installing a new security certificate on your customer's website might be causing the callback failures you're seeing. Here's why:
Callback Failures: The emails indicate that the callback URL (http://www.xxxxxx.co.uk/modules/gateway/WorldPay/return.php) is failing to receive a response from WorldPay after a transaction. The error code 301 suggests that the request is being redirected to a different location.
New Security Certificate: When you install a new security certificate, it can cause temporary issues with established connections, especially if WorldPay's servers haven't been updated to recognize the new certificate.
