Checkout Blocks sales channel
Behind the scenes, Checkout Blocks functions as a Shopify sales channel. This has a number of benefits while also imposing some unique requirements that a normal Shopify app does not face.
Only products made available to the Checkout Blocks sales channel will show up within checkout. You can add or remove products from Checkout Blocks within Shopify's products page. Learn more about adding products to sales channels.
Products that show up in Blocks on the checkout page must also be published to the online store or customers will be unable to add them to their cart.