Default , the scale barcode prefix of openpos is “20”. To change this, add this shortcode to yourtheme/functions.php or any snippets plugin

function op_custom_pos_weight_barcode_prefix($session_response_data){
    $session_response_data['setting']['pos_weight_barcode_prefix'] = '99';// change to number as you want
    return $session_response_data;
}
add_filter('op_get_login_cashdrawer_data','op_custom_pos_weight_barcode_prefix',12,1);