A payment gateway integration failure is one of the worst kinds of bug, because it's often silent from the store owner's side — orders just don't come in, with no error message pointing at the actual cause. Here's what we specifically check for before any store goes live.
Test mode left on accidentally
This sounds obvious, but it's one of the most common launch-day mistakes: a gateway left in sandbox/test mode after go-live, meaning real customers can "complete" a purchase that was never actually charged. We explicitly verify live-mode credentials as a pre-launch checklist item, not an assumption.
Currency and tax configuration mismatches
A gateway configured for the wrong currency, or a tax calculation that doesn't match your actual jurisdiction's rules, causes failed transactions or, worse, incorrect charges that surface as customer complaints and refund requests later.
Webhook and confirmation failures
Payment confirmation often depends on a webhook — a background notification from the gateway to your store confirming payment succeeded. If this isn't configured correctly, a customer can be charged while your store still shows the order as unpaid or missing entirely, which is confusing and damaging for both sides.
Failed transaction handling
What happens when a card is declined? A well-configured store gives a clear, specific message and an easy retry path. A poorly configured one shows a generic error that makes the customer assume the store itself is broken.
Why we test with real transactions
Test-mode transactions don't always catch these issues. Every store we launch gets a real, small live transaction tested and refunded before we consider a payment integration complete — it's the only way to be certain the full chain actually works end-to-end.