You cant login from this ip address

how can i fix this issue. i tried to solve it with the owner and on my own (i am a admin in the server) but i couldnt figure out how to solve the issue. I also googled it up and saw it had something to do with cmi (a plugin that we use on the server) but when i tried this i kept getting the same error.

(i tried using the /lockip (playername) thingy)

spigot/paper/bukkit