Connecting a product to the systems a business already runs on, so numbers match in both places and nobody retypes anything.
The integrations that decide whether a product is usable day to day.
A form submission becomes a lead with its source attached, and status changes flow back — so marketing spend can finally be judged.
Stock, prices and invoices synchronised with the system of record, so the site never sells something that does not exist.
Acquiring, refunds and reconciliation built idempotent, because retried requests must not charge a card twice.
Delivery, messaging, analytics, document services — wrapped behind our own interface so a provider can be swapped without a rewrite.
Assume the other side will be slow, wrong or down — then design for it.
Which system is the source of truth for each field, and what happens when they disagree. Most integration pain is an unanswered version of this question.
Queues, retries with backoff and a dead-letter queue a human watches, so an outage on their side delays data instead of losing it.
Scheduled comparison between systems with mismatches surfaced in a report, rather than discovered by a customer.
Not an exhaustive list — if it has an API, ask.
Tell us which systems need to agree. We will map the data flow and quote against it.