How to variables in log stash http output

[rkhapre (RK)]

@rkhapre

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

This message is Raw payload, i cannot change it to format => "json"
if i am making it json then also its not working

You have any working example with http output. Please suggest that