Within Etsy you will need to add SKUs to your products, this is because products lacking SKUs can result in errors and we may be unable to pull in your products and apply them to each of your shipments.
To be able to add products you will first need to login to Etsy and locate the "Your Listings" page within the dashboard.
Once hear click on the product you would like to add an SKU to, in this case it will be the Shiptheory product.
Once here you will want to scroll down until you find the SKU within this page. From here you can include an SKU of your choice as long as each product has a unique SKU.
Once done you will want to hit "Save" and then attempt to send through a new order to Shiptheory with the included product to ensure this is all set up correctly.
If you run into issues with adding SKUs and require additional support you can reach out to the Shiptheory support team here!