Some users may experience an error when booking in with Amazon shipping:
Amazon: (500) InternalFailure: We encountered an internal error. Please try again.
In this instance you want to try and periodically retry the shipment for this to eventually go through.
If this error persists after a couple of hours have passed please don't hesitate to get in touch with us at [email protected] or call us at 0117 403 4313, from there we can reach out to Amazon on your behalf.