URL rewrite rule

    function custom_rewrite_rules() {
            add_rewrite_rule( '^product_brand/([^/]+)/page/([0-9]{1,})/?', 'index.php?product_brand=$matches[1]&page=$matches[2]', 'top' );
            add_rewrite_rule( '^product_brand/([^/]+)/([^/]+)/page/([0-9]{1,})/?', 'index.php?product_brand=$matches[1]&product_cat=$matches[2]&page=$matches[3]', 'top' );
            add_rewrite_rule('^product_brand/([^/]+)/([^/]+)?', 'index.php?product_brand=$matches[1]&product_cat=$matches[2]', 'top');

            add_filter( 'query_vars', function( $vars ){
                $vars[] = 'product_brand';
                $vars[] = 'product_cat';
                return $vars;
            } );
     }
     add_action('init', 'custom_rewrite_rules');

and pagination

add_action( 'pre_get_posts', function() {
 $page = get_query_var('page');
 $query->set( 'paged', $page );
 return $query;
} );