What do the server logs say? Often a SOAP server will require a SOAPAction HTTP header be sent along with the POST body. See http://www.w3.org/TR/2000/NOTE-SOAP-20000508/#_Toc478383528.

To answer your second question, try dumping the POST data with

$q->param('POSTDATA');
[download]

See http://search.cpan.org/~lds/CGI.pm-3.43/CGI.pm#HANDLING_NON-URLENCODED_ARGUMENTS

Disclaimer: I've written a number of SOAP clients and servers, but none in Perl for many years.