Seal Subscriptions is a popular app which provides subscription capability for your Shopify store.
Replo supports using Seal Subscriptions in Replo pages, sections, templates, etc. To learn more about how to configure Seal, see Subscriptions and Selling Plans.
Seal provides a subscription box widget which it can embed directly on your page. This is usually see on Product Templates. If you want to allow Seal's embedded widget to select selling plans on your Replo page, make sure to toggle on the "Allow third-party embeds to select selling plan" toggle. More details at Allowing Third-party apps to override selling plan selections.