Webhook
also: webhooks, webhook endpoint, webhook url
A way for another service to notify your app automatically when something happens, by sending a message to a web address you gave it.
An HTTP callback. You register a URL with a service like Stripe, GitHub or Shopify, and it sends a POST request there when an event occurs. Your endpoint should verify the sender's signature, respond quickly, and handle duplicate or out-of-order deliveries.
Asking a shop to text you when your order is ready, instead of phoning every ten minutes to check. They contact you when it happens.
Payments, subscriptions and form submissions often arrive by webhook. When "the payment went through but the app didn't update", a webhook problem is a prime suspect.
Stripe is retrying the webhook because our handler times out. I'll save each event to a queue first, then return 200 and process it in the background.
Set up the Shopify order webhook. Verify its signature so we know it really came from Shopify, ignore duplicate events, and log each event so I can see what arrived.
Assuming each webhook arrives exactly once and in order. Services retry, so the same event can arrive twice, or late.