I received the error: “The variant ‘x’ already exists”

The notification “We received an error from Shopify while adding a new variant to SKU IQ Product #xxxxxx - The variant ‘x’ already exists” is the most common error. 

This error usually occurs when a merchant has two variations with the same color and no size. Shopify rejects the variation unless you specify a size attribute that allows the end customer to differentiate between the variations. If you see "The variant 'Default' already exists," it means that you don't have a size and/or color specified for the variant. If the products don't have an attribute specified, Shopify adds the "Default" attribute.

To avoid this error, you’ll need to define unique attributes for each variant, i.e. each variant must have a different color and size combination, and must not be left blank.