Active Resource custom method using POST

I've written a small piece of code that is supposed to place an order
in a order handling system. get, put and delete functions are working
great but I cannot get post to function at all... the error I get back
from the code below is 400 (bad request). I think it has something to
do with the headers but I don't know how to get more info out of this.
Is there a problem with the way I am handling the post method?

Thank you for your input!!

I may just go to the command line with curl - that seems to work
without a hitch.
Also, for anyone looking at creating a POST body, the code I posted
previously for converting a hash to POST body can be completely
replaced with {hash}.to_param. In my case:
body = input.to_param

Good luck -