"Since Akeeba Backup 3.5.0, you are not supposed to use the backup.php script file inside Akeeba Backup's directory. Instead, please use the akeeba-backup.php file located inside your site's cli directory.
This file is going to be removed in Akeeba Backup 3.6.0."
I don't know how to "use" the correct file, is there a pointer, or configuration file I need to edit? I am up to date with 3.5.1