Application access log is not logging the actual XFF of the real machine

In application access log nginx should print actual machine ip from where the request is coming. But instead of printing the actual XFF it printing some remote client ip which we are not sure from where it is coming.
Tried several way by chaging the nginx.conf file to print the actual machine XFF value. But still it is printing the remote cilent ip.
Any help should be highly appreciated.

P.S. - Server is running on AWS.