Application Approved But documents needed ?

[rajpalneha36]

Hello Guys,
with all your support , my application got approved today. return fedex tracker has not been activated yet.
But when i checked status of my application ,
Final Decision says "application has been approved" but under review of submitted documents: we need additional document from the applicant"
why is this so that they need more document also how to know which documents are needed and where to send them

http://imgur.com/a/uxACh

there is no request letter. and status says "action required"