The rate of access to this resource exceeds the prescribed limits.
Possible Causes
Your application is opening, reading or querying a single Sync object or its sub-items too often.
Your application is updating a single Sync object or its sub-items too often.
Your application is creating new Sync objects or their sub-items too often.
Possible Solutions
Analyze your application to ensure that the sustained rate of reads and writes against a single Sync object, and the sustained rate of of new object creations, is below 20 per second during normal application activity. Note that this limit only applies to explicit reads or writes; delivered state updates are not limited.
Analyze your application to ensure that bursts of activity are uncommon; Sync provides a ten-second burst window during which you can exceed the sustained request-rate limits.
Make sure your application (client or backend) uses a good exponential back-off algorithm like the one advocated by Amazon to retry on HTTP 429 (rate limiting) responses.