The error "must be unique" appears when I set a rule on the firewall.

You cannot set the rules on the same port. Also you need to set a rule on the port in the ascending-order.

If you set a bigger number of port before a smaller number, it will be an error by matching the beginning of number.

e.g. If you set port 6221 before 21 and 22 and 622, your will receive an error.