When using WorldPay as your payment gateway, you may receive notification from your WorldPay account of an order being processed but it does not appear as a completed order in your Shift4Shop store.
To correct this, you will need to specify a "callback URL" on your WorldPay account that redirects the order back to your Shift4Shop store. This callback process finalizes the order and sets it as "New" on your Shift4Shop store so you can process and ship the order to your customer.
The callback url you will need to use is as follows:
Be sure to use your Shift4Shop's store secure URL. If you do not know your site's secure URL, log into your Shift4Shop Online Store Manager and navigate to Settings > General > Store Settings, and look toward the section where the Store and Secure URLs will be listed for you.