Hello!
So, you need a Lua script file as a filter to filter out your response body's content and send to the user?
Guess, you got the right guy here, send me a message, we will discuss more about it.
People who are bidding has no idea about HAProxy and relation with Lua and response body, just bidding like a bot.
Anyway, send me a DM, so we could discuss about it. Did you install the filter lua dev version or still using buildin plugins?