Whitelabel NFT marketplaces can be integrated with existing e-commerce platforms and payment gateways through API integration, which allows for a seamless user experience. Developers can create APIs that enable the secure transfer of data between the NFT marketplace and the e-commerce platform or payment gateway. This integration allows for easy and secure transactions, as well as the ability to manage inventory, shipping, and other e-commerce functions. The use of existing payment gateways also helps to build trust and confidence among buyers and sellers, as they are using a familiar and secure payment platform. Overall, API integration enables a streamlined user experience and enhances the overall functionality of the NFT marketplace.