Scenario:
If a vendor is nearing the number of calls or bandwidth limit, the API must trigger email notifications to the vendor.
(API usage must not exceed 5,000 calls and 50,000 kilobytes of bandwidth per hour per vendor.) In Azure API Management (APIM), policies are a powerful capability of the system that allow the publisher to change the behavior of the API through configuration. Policies are a collection of Statements that are executed sequentially on the request or response of an API. Popular Statements include format conversion from XML to JSON and call rate limiting to restrict the amount of incoming calls from a developer. Many more policies are available out of the box.
References:
https://docs.microsoft.com/en-us/azure/api-management/api-management-howto-policies