You can provide a list of Shopify SKUs to be whitelisted for shipping via FBA. Only these SKUs will be shipped via FBA while any other SKUs will not be attempted for FBA shipping.
When no Shopify SKUs are added to the whitelist, it means all SKUs are whitelisted by default.
If a Shopify SKU is added to the whitelist as well as the blacklist then it will not be shipped.
If a multi-item order contains a few whitelisted SKUs and a few other SKUs, then only the whitelisted SKUs will be attempted to be shipped via FBA.
You have the option to add SKUs to the whitelist in bulk via CSV. When you upload an SKU list via CSV, it will replace all the existing SKUs in the whitelist with this new list.