Dynamically assign marketplace specific EU/UK VAT/IOSS numbers for seller fulfilled orders

[markber]

With the new VAT rules that have gone into effect Jul 1, 2021 in the EU and UK, this poses an interesting challenge for seller fulfilled orders, as marketplaces such as Amazon, eBay etc are collecting VAT upfront on orders shipping to the EU/UK, but a seller needs to include the marketplaces VAT/IOSS number on the customs declaration form, to ensure the customer isn't double charged when the shipment arrives in their country - since the VAT number will be missing from the customs form. Amazon appears to have updated their MWS API to now surface their IOSS number for eligible orders: https://sellercentral.amazon.com/forums/t/starting-july-1-2021-the-european-union-will-implement-new... Since ShipStation is already using the MWS API to import orders, this information is available, but currently isn't imported along with the order info. It'd save a lot of headache and extra steps for sellers if this info could be auto applied to customs declaration forms, rather than have to figure out the respective VAT info per marketplace. I can only imagine that other marketplaces will be doing the same thing.