This sounds odd.  I also don't understand from the description above how I am supposed to create the POST request. Are these http parameters? If so in which Conytent-Type format? It says above that it is "pson" (as opposed to say application/x-www.form-urlencoded, or multipart/form-data. 

An example of a POST would be good - something like the below? (guessing)

<pre>
POST /path/blah HTTP/1.0
From: kermit.thefrog@foo.bar
Content-Type: ???
Content-Length: ???

facts_format=pson&facts=<See Note>&transaction_uuid=<See Note>
</pre>