The Rich Returns API employs a number of safeguards against bursts of incoming traffic to help maximize its stability.
Users who send many requests in quick succession may see error responses that show up as status code
429. We have several limiters in the API, including:
A rate limiter that limits the number of requests received by the API within any given second. For the Returns API, we allow up to 2 requests/second, merchants on Custom Plans are limited at 4 requests/second.
A concurrency limiter that limits the number of requests that are active at any given time. Problems with this limiter are less common compared to the request rate limiter, but it is more likely to result in resource-intensive, long-lived requests such as sending emails or creating prepaid labels.
Treat these limits as maximums and don’t generate unnecessary load.
We may adjust limits to prevent abuse or enable higher limits for well-behaved high-traffic accounts.