Not all products are eligible for Stickerless Commingled Inventory. Most notably in grocery, health and beauty, and media products must always be labeled. Amazon is always evaluating categories and products and may change the eligibility for products at any time.
Add the item to the FBA Shipment in SellerCentral. After adding the item the following message may be returned (along these lines): This product is not eligible for stickerless, commingling. This product requires labeling to be received at our fulfillment centers. Select: “I agree to apply labels to these products.”