A 429 status code is returned when your request counts exceed our limit.
Here is a great reference that includes details on EPS traffic management as guidance on traffic ratios:
http://developer.ean.com/spec/. This guideline is intended to help you plan your API utilization.
Often, partners that receive this error message have built some form of brute-force cache of all hotel prices/dates with no actual traveler shopping. This remarkably increases the API utilization without actual revenue generation. As long as you are not utilizing our API in this manner, you should not receive this error. EPS suggests calling our API when a live traveler is visiting your site, rather than attempting to replicate our highly complex inventory systems through automated API traffic.
In the few cases when your calls become excessive, our global throttling mechanism on your CID will take effect. Our throttling mechanism is dynamic and responsive and can be triggered not only by traffic but other aspects in the system. When you get throttled, you will receive these header messages:
HTTP/1.1 429 Too Many Requests Content-Type: text/html Retry-After: 30
The body of the response will contain this text:
“Too Many Requests The user has sent too many requests in a given amount of time.”
If you receive this message, please attempt to scale back your requests, if possible. If you feel you have received this message in error or would like to discuss strategy around reducing your traffic load, please contact your EPS representative or raise a case.