You need to write "Content_type" => '...' instead of Content-type. Update:
Perhaps you consider to write:

use HTTP::Request::Common;
$req = POST 'http://www.receiver.com/hello.aspx',
  Host         => 'www.receiver.com',
  Connection   => 'Close',
  Content_type => 'application/x-www-form-urlencoded',
  Content      => [ Data => $pData ];
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or (looks more correct to me ) maybe

use HTTP::Request::Common;
$req = POST 'http://www.receiver.com/hello.aspx',
  Host         => 'www.receiver.com',
  Connection   => 'Close',
  Content_type => 'application/x-www-form-urlencoded',
  Content      => [ ID => 'Test', Len => $len, Data => $data ];
[download]