const token = generateToken(user); ^ TypeError: generateToken is not a function how to fix this?

I am trying to do jwt authentication but, I am getting the following error, how to fix this?

const token = generateToken(user);
                       ^
TypeError: generateToken is not a function

user.js

const generateToken = require('../utils/generateToken')
router.post(
   '/signup',
       userHelpers.doSignup(req.body).then ((response)=>{
         req.session.loggedIn = true
         req.session.user=response
         let user=req.session.user._id;
         // user id getting no problem 
         const token = generateToken(user);
         // here comes the error 
         console.log({token})
         res.json({token})
         res.redirect('/')
   })
  }
})

generateToken.js

const  jwt  = require ('jsonwebtoken')
function generateToken(id) {
    return jwt.sign({id}, process.env.JWT_SECRET, { expiresIn: '1d' });
  }
 module.export = generateToken

In generateToken.js, there is a logic for jwt.sign. how to fix this error?