We sometimes face the throttling response although we are not making concurrent requests and the request rate is low (we still developing the application calling the Pilot environment).
429 The API client is making too many concurrent requests, and some are being throttled. Throttled requests can be retried (with an updated request Date and HTTP signature) after a short delay.
What is the throttling threshold?. And what is the time period after which we should try again in case we exceeded that threshold?.
We get 429 response when there are too many concurrent requests .however the exact throttling limits may vary over time to adjust for available capacity on the platform.
To give you more insight about this error response i have attached a document(quality-of-service.pdf) which will be of help for you.This is a excerpt from our standard documentation.
Hope this helps