need the number of seconds since....

This line is failing:

$data['date_time']=random_bytes(8);  //this is to create a unique number

When I step through this line with the debugger, the code just crashes. (ie it gets stuck at this line). I am getting this apache error:

 PHP Fatal error:  Call to undefined function random_bytes() in C:\\xampp\\htdocs\\sub_crud\\application\\controllers\\Subit_backend.php on line 364

proof that an old dog can learn new tricks