1) Allow users to type in a discount code 2) Allow users to add multiple products to checkout. 3) Some sort of Shopify integration. I'm moving all my digital products over to Shopify's Starter Plan for this reason. I hate splitting things up and would love ConvertKit to be my one-stop shop for email marketing and basic e-commerce. Not being able to market a discount code (or a universal discount code that works on any product) and making people go through individual checkouts for every single product is costing me sales. It's asking the customer to do too much. Shopify's Starter plan is very simple, but it at least lets me do those two things, as well as send out abandoned cart emails, which is huge.