Generally, when a user visits a website with LaterPay integrated into it following events take place:
User visits a paid content page on merchant’s website.
Merchant checks if user has purchased access to this page with LaterPay. This step consists of:
Merchant shows the paid content page to user who has access to it and presents purchase buttons/links to a user who does not have access.
In practice the implementations are free to decide on the details of the last 2 steps and following integration flows emerged.