empty content returned

i am able to load and edit a doc using regular form submission and redirection

<form method="POST" action="http://export.writer.zoho.com/remotedoc.im?apikey=hiddenkey123456678&output=editor" enctype="multipart/form-data" target="_self">
File : <input type="file" name="content" size="38"> <br>
<input type="hidden" name="filename" value="'test.doc">
<input type="hidden" name="saveurl" value="storage/mydocument.doc">
<input type="hidden" name="id" value="12345678">
<input type="hidden" name="format" value="doc">
<input type="submit" value="Edit" class="divbutton" name="submit">
</form>

but however, remote posting from the server returns empty content, although i am able to get a valid 200 response from zoho servers. Any idea whats the cause?
'_rc' => '200',
'_content' => 'URL=null

the code snippet i use is as follows:

my $res = $ua->request(POST 'http://export.writer.zoho.com/remotedoc.im?apikey=hiddenkey123456678&output=url',
Content_Type => 'form-data',
Content => [file => ['test.doc'] , filename => 'test.doc', saveurl => '/storage/mydocument.doc', id => '124345678' , format => 'doc']
);