To resolve this error message (The remote server returned an error: (400) Bad Request.) when dispatching orders for Magento (Regardless of the courier) please follow the steps outlined below:
Click Connect then Order Integration.
Next, click Magento.
Click Edit on the connection you want to update.
Click on the Advanced tab.
Turn on the Use ParentOrderItemID in shipment notification instead of OrderItemID toggle.
Save the change.
Test with an order by despatching it in Mintsoft and checking Magento to see if it has been despatched or not.
If you continue to get the same error message as above, please raise a new case online and reference the title of this article.