Hello @akshatpandey36 ,
Did you check if your headers x-dynatrace.* are allowed via Loadbalancer (F5)?
Please find this link Firewall constraints for RUM | Dynatrace Documentation
You have also to ensure where you will store your request attribute, "capture server side" wildly used and enough. Also about HTTP method POST or GET.
It is not mandatory to use , to the letter, x-dynatrace-test, feel free to use x-dynatrace-yourvalue.
yourvalue = name of your app and environment for instance.
Some useful links :
JMETER integration : Dynatrace and load testing tools integration | Dynatrace Documentation
Capture request attributes based on web request data | Dynatrace Documentation