This error (Error An Error occurred when trying to Create Shipment - Error Message: The remote server returned an error. (503) Server Unavailable.) from DPD would be down to the product being marked as Packaging. Please review the product on the order and untick the Packaging toggle within the product settings before trying to generate shipment again.
Click Products then Overview.
Search for the products on the order.
Click Action and then Edit.
Click on the Extra Details tab.
Turn off Packaging toggle and save the change.
If you continue to get this error message after turning off the Packaging toggle, please reach out to the courier to check if they are aware of any issues with their servers.
If there's anything you need from the Mintsoft support team following this, please raise a new case online and reference the title of this article.