Use of X-Forwarded-For header

I was trying to test the behavior detection feature with API call /{{url}}/api/v1/authn.

As per the document i have added the X-forwarded-header with an IP address but logs shows my machine IP address instead of one in Xfowardedfor header value .

I have trusted application run behind proxy with loadblancer. Each time it gets the LB IP address instead of users IP address. any Idea how we can achieve the right client IP address?