Our app uses Shopify's store accounts to track purchase history. When a customer purchases an item tagged to provide access to the stream, that purchase is added to their account. When they access the stream page, they're immediately granted access – no special or unique link required.
Additionally, you can use the Orders menu item on the lefthand navigation to search for a customer by email address or order number. Once you've found the customer, you can use the paper airplane icon to resend their confirmation email.