Custom Shopify Subscription Setup

I’m running an existing Shopify store and want customers to subscribe to any product instead of only buying once. The goal is to introduce true recurring-payment functionality that works across the entire catalogue, with the flexibility to create and manage several plan options (e.g., monthly, quarterly, annual).

Here’s the scope in plain terms:
• Modify the theme and any relevant Liquid templates so every product page, cart, and checkout can toggle between one-time purchase and subscription.
• Write or adapt a custom Shopify Script / Function that talks to the Subscription APIs and handles charge scheduling, automatic renewals, and plan-specific pricing or discounts.
• Surface a simple customer portal inside “My Account” where shoppers can pause, skip, swap, or cancel their active plans.
• Ensure the admin side lets me add, edit, or retire plans without touching code.
• Provide clear documentation and test transactions so I can see renewals firing correctly in Shopify Payments.

Tech you’ll likely lean on: Liquid, JavaScript, Shopify Subscription APIs, Checkout UI extensions, and the Script Editor or Functions framework. If you prefer an app-based helper that still needs custom code, let’s discuss.

Deliverables will be considered complete once:
1. Any product can be purchased on at least two different subscription plans and renews automatically.
2. Theme displays pricing, savings, and next-charge dates accurately.
3. Customer portal actions sync instantly with Shopify’s backend.
4. You hand over commented code plus a short setup guide.

If you have previous live examples of recurring-payment builds, send a link or brief description when you reply.