Zoho email search API: additional search criteria not in effect

Zoho email search API: additional search criteria not in effect

Addition search criteria on Zoho Mail API are not working. 

URL:  https://www.zoho.com/mail/help/search-syntax.html

I am trying on URL with 

http://mail.zoho.com/api/accounts/<AccountId>/messages/search?searchKey=subject:<subject>:and:is:unread

I even tried with encoded url.