Fondy payment integration in Shopify — auto-redirect with order

Task: when clicking "Pay now" in Shopify → auto-redirect to Fondy
with the exact order amount, no manual input.

Problem: window.Shopify.checkout deprecated since August 2025,
Additional Scripts blocked in new Checkout Extensibility.

Solution:
— Checkout Blocks Custom HTML + Liquid {{ checkout.total_price }}
— Vercel serverless function (Node.js) → Fondy API
— SHA1 transaction signature, unique order_id per transaction
— HTTP 302 redirect to Fondy checkout with correct amount
— Full flow without manual input, tested end-to-end

#shopify #fondy #payment #vercel #nodejs #javascript