You can use the following commands in-game as OP to ban/unban players on your Minecraft Server.
Commands can be run in the multicraft console too, make sure to remove the / when running commands via ths console.
Ban players
/ban username reason - bans a player by their username, stopping them being able to connect, adding a reason is optional.
/ban-ip username reason - bans a player by their Ip address, stopping any player with this IP being able to connect, adding a reason is optional.
Unban players
/pardon username - unbans a player, allowing them to connect.
/pardon-ip IP address - unbans an IP address (only valid IP addresses will be unbanned, not players’ usernames)