Reading the code, you need to type the command in uppercase for it respond:
if(msg.content.toUpperCase().startsWith(process.env.PREFIX)){
//await handler.handle(msg, client);
}
Does this code happen when the bot is ready?
console.log(`${client.user.tag} is ONLINE :)`);
Do you see <CLIENT.USER.TAG> is ONLINE :)
in the logs?