Walmart requires a Product Identifier for every item created. To understand what a Product Identifier is, please see What are UPCs, EANs, ISBNs (GTINs) and ASINs?

There are circumstances where you can apply for an exemption from this requirement. For example, if you would like to sell jewelry pieces on Walmart.com that do not have Product IDs (e.g., private label or handmade jewelry), you can request special authorization to sell these items. 

To request a UPC Exemption, create a case by selecting Items > Item Setup > UPC Exemption Request in your Walmart Seller Center.