The Variant ID field is used to group child skus together. Retailers will want to use the same code/value on all skus you want to appear on the same PDP.
Example
Mens Sweatshirt
Available in Black and Gray
Sizes: S - XXL
*Brands will use the same Variant ID code for each of the size/color variants so that all will show up on the same PDP on live site.
Please be advised once a grouping has been published in the ShopSimon™ Portal, skus cannot be moved from one grouping to another. The only way to 'reorganize' sku groupings is to delete and reload the product data.
Please contact the ShopSimon Operations team at sellersupport@shopsimon.com for more information on this topic.