用户代理标头未通过API端点

I have and API created (In development and can't share the endpoint but when I am curling it with the specified headers:

-H 'Pragma: no-cache' 
-H 'Origin: http://dev.symposeum.com' 
-H 'Accept-Encoding: gzip, deflate, sdch' 
-H 'Accept-Language: en-GB,en-US;q=0.8,en;q=0.6' 
-H 'Authorization: Bearer f4e73ac041d19037b89e8791cfe2f07201f7dfc8' 
-H 'Accept: application/json' 
-H 'Cache-Control: no-cache'  
-H 'Connection: keep-alive' 
-H 'Referer: http://dev.symposeum.com/'

It works fine but when I pass the user agent header along with these headers which has to be passed I guess, it works on only a few system not all. It is a live deployed site.

The user agent header being:

-H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.106 Safari/537.36'

Can someone help in this regard or at least try to explain why this is happening ?