Polling
Your application asks every X minutes what has changed. It’s simple and robust, but there is always a delay, and lots of useless calls.
Webhooks
The source system notifies you as soon as an event happens. It’s fast and economical, as long as you handle lost, duplicated or out-of-order messages.
Often, both
We usually combine webhooks for responsiveness with a periodic check to catch anything missed. It’s the basis of our CRM & ERP integrations. See also: defining the source of truth.