Drupal Commerce error message fix.

We need a fix for an error message that is popping up when adding item to cart. Please go to https://www.moureys.com/pickup-and-delivery/schedule-pickup/demand-pickup. When you try adding an item to the cart you will see the following error message "The website encountered an unexpected error. Please try again later." Not sure what has gone wrong. The online store is run on Drupal Commerce.