I'd be inclined to loop "for ever":

    while (1) {
        #  Get web page
        my $response = $ua->post( $page, \%form );
        
        #  Check for errors
        if ($response->is_success) {
            $data = $response->content;
            return \$data;
        } 
        
        sleep 100;
    }
[download]

That is then easy to turn into a loop for some maximum number of times with error handling by falling out the bottom of the loop.