The problem is not in your code, but rather in parameters provided to 'search.cgi'. Although HTTP::Request::Common want to array reference not hash reference as parameter to 'POST' sub, there is no difference in the server response

my $Page = $Browser->request(POST $URLtoPostTo,[%Fields]);
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Make sure that you pass all parameters as webform do. If it doesn't help than take a look on cookies and agent specification