You can check the problems for shipping plan by using the following self-service tool.
Amazon systems are barcode-driven. Each product you send to a fulfillment center requires a barcode so that it can be tracked throughout the fulfillment process.
Label Products is the third step in the six-step shipment creation process:
Products that do not qualify for Stickerless, Commingled Inventory must have FBA labels in order to be received at Amazon's fulfillment centers. By selecting the Labeling required filter on the Label Products page, you can view the products in your shipping plan that require labels. For products that require labels, you must affix a label to each unit of the product, and the label must cover any existing barcodes.
You have several options for printing product labels:
If you have selected Amazon in the Who prepares? column of the Prepare Products page for a given product, then you will be required to use the FBA Label Service, and "Amazon" will be automatically applied to the Who labels? column. If you are prepping a product yourself, then you may still use Amazon Labeling by selecting "Amazon" in the Who labels? column on the Label Products page. Labeling fees will apply to all units that Amazon labels.
Amazon can only label products that have an product identifier (UPC, EAN or JAN) on the product itself. See FBA Label Service for additional information and fees.