Adding a new carrier to your Shopify store is one of those tasks that feels complete the moment the credentials are saved and the first test rate shows up at checkout. The gaps in Shopify shipping integrations almost never appear during setup; they appear on the first real orders, in front of paying customers, at the worst possible time. A tracking number that syncs to Shopify but the customer notification never fires. A rate that is correct for a standard domestic order but silently falls back to a flat rate for anything unusual. This checklist covers every layer of Shopify shipping integrations with specific things to verify.