What is API

Where an API helps a business

• A lead from the website or a bot lands in the CRM and a spreadsheet by itself, with nobody copying it.
• After a payment, a bot extends access in another system on its own: a VPN panel, a customer account, a service.
• You want to hear about a marketplace event before your manager does: a delivery slot opened, an order arrived.
• A website or app shows data that lives elsewhere: the catalogue, stock, a user profile.
• Two of your services must work with the same data instead of keeping two copies that drift apart.

Types

• REST API: every entity has its own address, with requests to get, create and change it. Marketplace APIs, the Marzban panel and our online stores work this way.
• Webhook: the other direction, where the service sends an event to your address itself. Use it when an instant reaction matters.
• Scheduled polling: when a service has no webhooks, your program asks the API every few seconds.
• Internal API: between your own services, closed to the outside world and protected with a shared secret.

How we use it

• For a Wildberries supplier, a bot polls the API every 30 seconds and sends a free delivery slot to Telegram with a direct booking link: slot monitoring.
• A lead from a Telegram bot goes through n8n into Bitrix24 and a Google Sheet, and a deal status change comes back as a webhook: lead automation.
• The Tech Poly VPN bot creates and renews users in the Marzban panel through its REST API, while it keeps money, terms and discounts itself.
• The account management bot has no database of its own: every action goes to the service's internal API with a shared secret in a header, so accounts live in one place.
• The online store storefront gets its catalogue and places orders through an API written in FastAPI.

Which of your systems can be connected is worked out in a free audit under Automation.

Common problems

• Two sources of truth. When data lives both with you and in someone else's system, the copies drift. In Tech Poly VPN the subscription end date is written to the bot's database only after the panel returns it, so the bot never treats a subscription as active when traffic is already cut off.
• Failure halfway. The payment is confirmed but the panel does not answer. You need a rollback: the request goes back to pending and the discount is not burned.
• Repeats. Two admins press Confirm at the same moment, or an event arrives twice. The operation has to be idempotent; in Tech Poly VPN that is a row lock in the database on confirmation.
• Someone else's service changes without you. YouTube changes its protection regularly, and the video downloader bot updates yt-dlp first when downloads fail. An integration with a third-party API needs maintenance.
• Keys and tokens. They belong in n8n or in .env on the server, not in the code and not in a workflow file.

When you do not need it

If data moves once a month and there is little of it, a manual export to a spreadsheet costs less than an integration. If a service has neither an API nor webhooks, any connection to it is fragile, and we say so honestly in the audit instead of promising to connect everything.