Error Code 8016
This error is caused because the data you provided to Amazon is insufficient to correctly create the variation relationship between your parent products and your child products. Repeating size or repeating color or one of the child products is missing size or color.
Check the items in the product bulk editor by choosing necessary fields. Or you can check by exporting the related fields. To solve this error, Amazon requests that you enter the same variation theme for the same family: e.g., size, color, sex, etc. Sometimes, Amazon wants you to enter color and size to the parent too. So, it will be best practice to enter color and size values to the parent item.