The error (An Error Occurred when attempting to: When Creating Intersoft Shipment Error:Attempted to divide by zero) when creating a shipment for Royal Mail can be caused by:
The only item on the Order is a Packaging item.
One or more of the Product's Quantity Allocated is showing as 0.
To check the Packaging toggle please follow the steps below:
Click Orders then Overview.
Search for the Order.
Select Actions then Details.
Click the Items tab.
On the SKU, click View Product.
Next, click Extra Details.
Switch off the Packaging toggle.
Click Save, then, retry the shipment.
To check if the Product's Quantity Allocated is showing as 0, please do the following:
Click Orders then Overview.
Search for the Order.
Select Actions then Details.
Click the Items tab.
Check that all products have a number higher than 0 in the Allocated column.
If it's 0 please click Remove and re-add the product back to the order.
Alternatively, if the product is out of stock you will need to book the required amount into your Warehouse before continuing.