You may not perform more than 20 requests per second per API key.
To stay within this limit, we strongly recommend that you use a library to help you orchestrate your request rate. It can be very helpful for the rate limiting framework of your choice to be backed by a system like Redis, that way you can ensure that you are staying below the limit across all of your apps that issue requests into AIQ Ecommerce. You should also favor sequential over parallel requests if you don't want to implement a sophisticated rate limiting system.
If you exceed 20 req/s, you will first receive a 429 error. Failure to slow down your request rate may result in a temporary ban. The headers X-RateLimit-Limit and X-RateLimit-Remaining are available to help you understand how many requests are available for a given rolling window period and how many are instantaneously remaining for you to make.