Which pattern can a web API use to notify its client of state changes as...

A web API can use HTTP Webhook to notify its client of state changes as soon as they occur. A webhook is an HTTP callback that allows an API to sendreal-time notifications to another system or application when an event happens. The client registers a URL with the API where it wants to receive notifications, and then the API sends an HTTP request to that URL with information about the event. References:https://docs.mulesoft.com/connectors/webhook/webhook-connector