Recently when whitelisting a number of IP addresses through UFW, I received this wonderful error that left me scratching my head...

ERROR: initcaps
[Errno 2] ip6tables: Chain already exists.

Through some research, I have found that UFW tends to freak out if multiple `ufw allow from x` commands are run in quick succession and can end up in a shitty state with duplicate entries.

Running the following command should resolve those issues and allow you to add in your entries. I'd recommend you allow 1 second between each command when adding entries to your firewall in the future!

sudo ufw disable
sudo iptables -F
sudo iptables -X
sudo ip6tables -F
sudo ip6tables -X
sudo ufw enable