If you're seeing this error (Error From Intersoft:Error Code:E1437 Description:The contact phone number is invalid) when trying to create a shipment with Royal Mail (Intersoft) then this would be due to an entry in your Warehouse settings where the contact phone number is either empty or has letters in. This field requires a phone number to be added to the field. To fix this, please follow the steps below:
Click Warehouse then Manage Warehouses.
Find the Warehouse that the order is coming from and click Edit
You will see the Contact Number field is either empty or has invalid characters in
Update the Contact Number and press Save.
Finally, retry generating the shipment.
If you're still having issues after having followed this, please raise a new case online and reference the title of this article.