Sometimes cron script properly configured and crontab added as well but in plesk control panel it shows the error which his.
“php: command not found

In order to resolve the issue the cron execute permission need to be correct, by using below command from ssh

/usr/local/psa/admin/bin/server_pref -u -crontab-secure-shell “/bin/sh”

O/P SUCCESS: Server preferences are successfully updated.