Here's my error.
Plesk Onyx 17.8.11 Update #49
fail2ban.action [10650]: ERROR iptables -w -n -L INPUT | grep -q 'f2b-apache[ \t]' -- stdout: ''
fail2ban.action [10650]: ERROR iptables -w -n -L INPUT | grep -q 'f2b-apache[ \t]' -- stderr: ''
fail2ban.action [10650]: ERROR iptables -w -n -L INPUT...