Getting 413/414 status code when working with amazon associates api

I'm trying cart create api to create remote carts on amazon. I'm able to create carts with 40 items. But, I'm unable to create carts with 50 items. I have read the documentation for same here, ref : http://ift.tt/1joWDuw

My curl requests are something like, curl -X POST --data 'data_in_compliance_with_doc'-H 'Content-Type:application/x-www-form-urlencoded;Accept-Language:en;Accept-Encoding:gzip,deflate;Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8;User-Agent:Mozilla/5.0(Windows;U;WindowsNT6.0;en-US)AppleWebKit/527(KHTML,likeGecko,Safari/419.3)Arora/0.6(Change: )' -v http://ift.tt/1NB50lC As per documentation you can create a cart for 50 items. But the response status code I'm getting for 40 items is 200. And for 50 items it's 413/414. What can be the reason? As per the documentation I should not be getting 'URI too long' errors, because the limit specified is 50.