Make sure to convert user input to lower case as well

index.js

@@ -117,9 +117,9 @@ async function ban(message) {
 
   const members = message.guild.members.cache.filter(member => {
     if (member.nickname) {
-      return member.user.username.toLowerCase().includes(message.content.split(" ")[1]) || member.nickname.toLowerCase().includes(message.content.split(" ")[1]);
+      return member.user.username.toLowerCase().includes(message.content.split(" ")[1].toLowerCase() || member.nickname.toLowerCase().includes(message.content.split(" ")[1].toLowerCase());
     } else {
-      return member.user.username.toLowerCase().includes(message.content.split(" ")[1])
+      return member.user.username.toLowerCase().includes(message.content.split(" ")[1].toLowerCase())
     }
   });