How a REST API works
REST is a convention rather than a product. It says: treat every piece of data as a resource with its own web address, and act on it with the ordinary verbs the web already has. A GET request reads a resource, POST creates one, PUT or PATCH updates it, DELETE removes it. Ask for a customer record and you get that customer; ask for the collection and you get a list.
Each request stands alone. The server keeps no memory of your last call, so every request carries its own credential and its own parameters. Responses come back as JSON with an HTTP status code attached — a success code, a refusal because the credential was wrong or the caller lacked permission, a not-found for a resource that does not exist. Those codes are the fastest way to diagnose a broken integration.
Why REST APIs matter
Because so many platforms follow the same convention, connecting them is a known job rather than a research project. Google Ads, Meta, Shopify, WooCommerce, Mailchimp and WordPress all expose REST-style interfaces, and a developer who has used one can find their way around another quickly. That keeps integration quotes sane.
It also means the tools in the middle can be generic. Zapier and Make work with almost anything precisely because most services speak this way, so a small business can join systems together without commissioning custom code for each pair.
Where REST APIs go wrong
The commonest failure is authentication, not logic. Tokens expire, permissions get removed when a staff member leaves, and a key created for testing quietly lacks the scope the live job needs. Read the status code before rewriting anything: a refusal is a credentials problem and a not-found is an address problem, and they need opposite fixes.
The second is pagination. A collection endpoint returns one page of results, not everything, so a report built without following the next-page link silently shows a fraction of the data and nobody notices because it still looks plausible. The third is calling too often and hitting a rate limit, which usually surfaces as intermittent gaps rather than a clean error.
How to act on it
Read the platform’s documentation before scoping the work, because it tells you what is genuinely available. Plenty of integrations are abandoned halfway when the field somebody assumed exists turns out not to be exposed at all.
Insist on logging every request and response, handling paginated results properly, and retrying a failed call rather than dropping it. Give each integration its own credential with only the permissions it needs, so one leaked key does not open everything. If you are joining a website to another business system, treat it as custom development work with testing time in the estimate, and be clear on how it differs from an event-driven webhook before choosing between them.