QuickBooks Online and QuickBooks Online API usage has continued to grow at a rapid pace. In order to continue providing a high quality service, Intuit has revisited throttling and rate limits announced in 2016. The enforcement of some of the limits had lapsed and will be re-instituted August 12, 2019.
Review the limits and throttles section of the developer documentation to ensure your application is in compliance. When throttling occurs, HTTP status code 429 will be returned. Observe the Retry-After header response when resending a request with the same requestId.
If you have any specific questions, reach out on our developer forums at developer.intuit.com/help.