For SellerCloud Support - App Setting "EnableSearsMatrixPosting" must be set to "True".
While sears attributes are not required for simple products, there are some attributes which are required for variation listings. Make sure to enable the client setting - Enable Sears Attributes.
Please Note: The children (variations) must be "Ready" and "Enabled" for Sears on their individual Sears properties page. This is because, unlike eBay, the individual variation is sent when posting the parent. Likewise, inventory is updated from the individual child product, not from the matrix parent.