This error occurs when the variant ID listed in the import sheet doesn't match the original variant ID in Shopify. It can also occur if the product hasn't been added to ReCharge yet.
If the product doesn't exist in a rulest, go ahead and add it to the ruleset and retry the validation.
If the product does exist in a ruleset, make sure you're using the original variant ID. Not the ID for the hidden "auto-renew" variant.