username and password invalid on cronjob setup through anacron on server control panel
Welcome to SE!  The message is &quot;Could not open input file&quot; so the problem is finding the files it needs to run, not the username/password.  What is 'my_php_script' in the cron entry?  Does the cron entry literally include '[mysite]' or is that where you have redacted your site name?
There are several ways to run scheduled jobs but I suggest you use the 'cv' method if you can.  See the documentation for details.
Administrator credentials will work, or you can set up a dedicated user for cron.