To sell print-on-demand t-shirts using X, choose a service like Printful or Printify to create designs and handle fulfillment. Set up a store with a compliant website (contact info, refund/shipping policies, secure checkout). Convert your X account to professional, use Ads Manager to create a catalog in Shopping Manager, and add t-shirts with details (title, price, images). Promote with high-quality pics, hashtags, and engagement—link to your store for sales. Boost success with contests, influencers, and X analytics.