I ran into this exact issue building my inventory sync app. The thing that tripped me up was webhook ordering during installation. You’ve got to deploy and test your webhook endpoint before creating the webhook through Admin API - otherwise you’ll get failed deliveries right away. Another gotcha: store the webhook subscription ID in your database for each shop. When merchants uninstall, clean up those subscriptions or you’ll hit rate limits with orphaned webhooks. This gets critical with hundreds of installs. For orders, I’d use orders/paid instead of orders/create - it filters out drafts and only catches actual completed transactions. Keep your server response under 3 seconds or Shopify’s retry system kicks in.