do it like this (make sure you delete path when done with it):
var path_array = ap_grid_path_array(obj_tester.grid, x, y, mouse_x, mouse_y);
path = path_add();
for(var i = 0; i < array_length(path_array); i++){
var point = path_array[i];
path_add_point(path, point[0], point[1], 1);
}
path_start(path, 3, path_action_stop, 0);