You built a Shopify integration. It works great. Until it doesn't.

A customer's network drops right after the checkout POST fires. They refresh. The browser retries. Shopify receives two identical order creation requests. You now have a double order, a double charge, and a very confused customer.

This is an idempotency problem. And it is more common than most Shopify developers expect.

What Is Idempotency in a Shopify Context?

An operation is idempotent if running it once or a hundred times produces the same result. In Shopify integrations, this covers:

• API mutations (order creation, fulfillment, refunds)

• Webhook processing (order.paid, inventory.update)

• Background job retries

• Third-party sync operations

Strategy 1: Use Idempotency Keys on REST API Calls

Shopify's REST Admin API accepts an Idempotency-Key header on POST requests.…