How to get the user id, username, nick when mentioned by another user

I tried

m.mentions.members.first()

m.mentions.members.first()

m.mentions.members.first()

m.mentions.members.first() but to no avail it didn't work as expected due to the

mentions

mentions

mentions

mentions property being

undefined

undefined

undefined

undefined despite mentioning someone. Any help would be appreciated!

Here's the brief code:

module.exports = {

    callback: async (m) => {
        
        let user = m.member.nickname;
        let mentionedUser = m.mentions.members.first();

        if ( mentionedUser === undefined) {
            m.channel.send("You need to mention someone!")
            return;
        }  
        m.channel.send(`${user} mentioned ${m.mentions.members.first()}`) //test      
    },
};

module.exports = {

    callback: async (m) => {
        
        let user = m.member.nickname;
        let mentionedUser = m.mentions.members.first();

        if ( mentionedUser === undefined) {
            m.channel.send("You need to mention someone!")
            return;
        }  
        m.channel.send(`${user} mentioned ${m.mentions.members.first()}`) //test      
    },
};

module.exports = {

    callback: async (m) => {
        
        let user = m.member.nickname;
        let mentionedUser = m.mentions.members.first();

        if ( mentionedUser === undefined) {
            m.channel.send("You need to mention someone!")
            return;
        }  
        m.channel.send(`${user} mentioned ${m.mentions.members.first()}`) //test      
    },
};

module.exports = {

    callback: async (m) => {
        
        let user = m.member.nickname;
        let mentionedUser = m.mentions.members.first();

        if ( mentionedUser === undefined) {
            m.channel.send("You need to mention someone!")
            return;
        }  
        m.channel.send(`${user} mentioned ${m.mentions.members.first()}`) //test      
    },
};