If you have received the rate_limit error message, you should limit background jobs, such as performing mass refunds, to a subset of the maximum. This allows for time-sensitive events such as live charges to succeed even with additional traffic.
If you expect to hit this limit regularly, see Scaling your API with rate limiters on the Stripe Blog with details on rate limiting strategies to help you avoid this error in the longer term.
Stripe has a rate limit of 100 parallel requests per second for live mode transactions, and 25 parallel requests per second for test mode transactions.