Uh you need to remove firewalld and such, fail2ban could be next to CSF. ( but could “conflict” or harder to find wich one has blocked a ip ) ( you can change the config using iptables right with csf and mail if blocking if wanted )
Is csf is blocking you can unblock in csf, if fail2ban you have to do there. so that is the most “conflicting” but if more conflicts please write here ???
So fail2ban is not blocking csf installations!
You need i guess all of the required IPTables modules installed if not there already.
For all of you have a look before uninstall and using csf only to the jail.local config file.
So you know more.