How to variables in log stash http output

Elastic Stack Logstash
3

I Also have similar issue with Logstash http output 5.x

where my message is like this

headers => {

         }
         format => "message"
	
   message => '{"ID":"%{ID}","requestNumber":"%{requestNumber}","requestTimestamp":"%{requestTimestamp}"}'

with this format, i am not able to get the http output
However if i try using the hardcode value in message, its working perfectly for me