Adding some wait time between API requests to avoid overloading the server
Create throttling for API calls is just one aspect of making your API integration resilient. There are many other types of failures to handle. Instead of weaving the error handling into your code, you should consider using something like Polly https://github.com/App-vNext/Polly
There a more details on it here http://www.thepollyproject.org/2018/03/06/policy-recommendations-for-azure-cognitive-services/