my $response = $ua->post(
    $url,
    'Authorization' => 'Basic QUM5YzFmZjJkMTg4MGU0YWZmOWQxNmQzYTAzM2I0
+NjMxYzplYmFjZTRhYmQ0ZmY1NGM5NDNlZGFlZTg0YjJhMGY0MA==',
    'Content-Type'   => 'application/x-www-form-urlencoded',
    'Content' => \%form, # note the backslash here!
);