The reference identifying the form fields and values for your POST request doesn't have to be a hashref. Usually I see this as an array reference specifically for this reason.

An example from the HTTP::Request::Common docs:

POST 'http://www.perl.org/survey.cgi',
     [ name   => 'Gisle Aas',
       email  => 'gisle@aas.no',
       gender => 'M',
       born   => '1964',
       perc   => '3%',
     ];
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