If you're integrating a gift card API for the first time, the vendor demo will look great. The sandbox will work on the first try. You'll think this is going to be a clean two-week sprint.

Then you ship to production and discover the same three problems every team hits:

Duplicate orders because retries weren't idempotent.

Missed transactions because webhooks didn't arrive.

A finance team that can't reconcile your numbers against the vendor's numbers.

I write a lot about gift card infrastructure (full disclosure: I work on a product in the space). The piece below is the developer-shaped version of a longer evaluation guide we published — focused on what actually breaks at runtime and what to ask vendors before you commit.

Idempotency, or you'll double-charge your customers If your POST /orders call times out, you don't know whether the order went through. So you retry.…