The API has a strict rate limiting system to prevent high loads on the server to try to make sure requests can be answered promptly. There is a default set of 180 requests per 15 minutes per collection for each organisation. If this limit is exceeded an error response will be returned with code 429 (see the error codes page for more information) for every request made until the 15 minute period ends after which data will be returned as normal.
In addition to the default and if you find this limit is not enough for your needs, you may want to discuss relaxing the limit with us as we can increase the requests per period or shorten the length of time the requests are made in if we believe there is sufficient reason to do so.