Any suggestions will be gratefully received. What follows is only for
anyone who would like to know, in detail, what's going on. My code is at
the bottom of this message.

Here's an overview of why I'm doing what I am: The site I'm trying to
automate is an EU governmental one. My employer has recently been hit
with a VAT bill because one of our customers de-registered for VAT early
last year and therefore we shouldn't be sending goods VAT-free. The
customer didn't tell us, and we're liable for unpaid VAT. Our government
site suggest regular checking of customer VAT numbers against the EU
database to avoid this. There is a module on CPAN that can give a
valid/invalid result for VAT details, but I want to capture the
certificate the site issues because it has a consultation number as
proof of checking the VAT status, without which the certificate is
useless, it could easily have been fraudulently made. The only part of
the data that's missing when I use mech is the consultation number, the
vital part that proves you did carry out the check.

The web-page that contains the form I'm mechanising is at
<URL:http://ec.europa.eu/taxation_customs/vies/vieshome.do?selectedLanguag...>
subsitute that last EN for your preferred language code, ES, FR, DE, DK,
etc., you can find the form in the source by searching on "viesquer.do".

The CPAN module that gets halfway there is
Business::Tax::VAT::Validation. I didn't discover this until I'd almost
completed my program, but it doesn't provide the consultation number
which can be used as a defence if challenged by the VAT authorities.

Here's the code I'm using, VAT numbers omitted for privacy, if anyone
wants to run this, and can't find any valid data to use, please let me
know by email and I'll send some data that works, I just don't want to
put other people's data 'out there':

my $cust = shift;
#       an array ref.   $_->[0] = our customer identifier - not submitted, just
#                                                         happens to be in the array.
#                                       $_->[1] = 2 letter country EU code
#                                       $_->[2]      = customer VAT number

my %requester = (
        state   =>   'GB',           #       2 letter country EU code
        vat_no  =>   '',                     #       a valid VAT number for the country
                                                        #               - removed for privacy reasons.
);

my $mech = WWW::Mechanize->new();

#       Set a sensible UA - don't want to be thought of as a bot
$mech->agent_alias('Mac Safari');

#       load the page containing the form
$mech->get($site_root);

#       fill-in and submit the form
$mech->submit_form(
        form_name       =>   'frmVat',
        fields  =>   {
                ms                              =>   $cust->[1],
                iso                             =>   $cust->[1],
                vat                             =>   $cust->[2],
                reqeusterMs             =>   $requester{state},
                requesterIso    =>   $requester{state},
                requesterVat    =>   $requester{vat_no},
                BtnSubmitVat    =>   'Verify',
                name                    =>   '',
                companyType             =>   '',
                street1                 =>   '',
                postcode                =>   '',
                city                    =>   '',
        }
);

return \$mech->content;
__end__

Thank you for any help you can give.

   Justin.

Firefox with the Firebug Plug-in might help you find if you're
sending values differently. You easily can see what's sent and the
response in the Console tab.

    http://www2.research.att.com/sw/tools/wsp/

It logs HTTP requests/responses in the form of Perl code (UserAgent).

Then we don't need to know what all the JS does, we just need to know
how to construct the request we want...

   Justin.

   Justin.

I hate how debugging takes 3 times (or more) the time it takes to code!

Anyway, thanks to Tad and J for their suggestions.

   Justin.