I see there are default commands already assigned to the list, however, if I add more to the list they are not getting blocked eg /kit so now the players go and duel and kit up during the duel.

Blacklist commands are enabled

Have you tried it yourself to see if it works? Right now it's case sensitive, so that could be the issue. The version below fixes that. Let me know if it solves the issue for you, or not.

https://pastebin.com/PeAvBSZt

Yes, I have added few commands like, "/tpb /buy /kit /tpr /tpa /recall /spawn" and everyone still can. I'll try the new one you gave and let you know. I kept all the commands lower case. The same as if you would have used them in chat

Merged post

It loaded version 1.21 however it didn't disable the commands thank you for looking into it
my config
"Settings": {
"Allow Announcement": true,
"Auto Create Dueling Zone If Zone Does Not Exist": true,
"Auto Enable Dueling If Zone(s) Exist": true,
"Blacklist Commands": true,
"Blacklisted Chat Commands": [
"/tp",
"/tpb",
"/tpr",
"/tpa",
"/kit",
"/remove",
"/bank",
"/shop",
"/event",
"/rw",
"/home",
"/trade"
],