The Import One-Stop-Shop (IOSS) is the electronic portal businesses can use to facilitate VAT e-commerce transactions when shipping internationally. The IOSS VAT identification number consists of 12 alphanumeric characters.
This number only applies to multi-vendor marketplaces that collect taxes on your behalf. These include Amazon, eBay, and Etsy. If you're running your own hosted shop on Shopify or Wix, the IOSS number is not applicable to your store.
In order to add IOSS number in Multiorders on your marketplace, go to the Integrations page.
If you have already connected your marketplace, go to the Connected Integrations area and on your marketplace window click on the Edit button:
An integration window will open where you can find the IOSS number field at the bottom. Enter your IOSS number and click on Save:
If you are just about to connect your marketplace for the first time, on the Integrations page go to the Add New Integration area, click on your marketplace and you can fill in an IOSS number on the integration form together with other details.