When creating listings using the Market Listings Add template, there is a certain format you must follow to create variation listings.
The first listing of the variation listing will act as the 'parent listing,' and will be the only listing that will have the parent fields filled out. All the listings that follow that will ONLY have the variation fields filled out, NOT the parent fields. See image.
Notice how the first SKU of each variation listing is the only one with the parent fields filled out, and all SKUs that follow only have the variation fields filled out. The parent SKUs in this example are 'shirt-red-large' and 'pants-blue-large.'