I have used this code for comparison.

UserSchema.pre('save', async function() {
    const salt = await bcrypt.genSalt(10)
    this.password = await bcrypt.hash(this.password, salt)
})

UserSchema.methods.comparePassword = async function(candidatePassword) {
    const isMatch = await bcrypt.compare(candidatePassword, this.password)
    console.log(this.password);
    console.log(candidatePassword);
    return isMatch
}

I always get an invalid credentials error from the below login function. I have checked by logging the outputs. The problem lies with the compare password functionality.

const login = async(req, res) => {
    const { email, password } = req.body

    if (!email || !password) {
        throw new CustomError.BadRequestError('Please provide email and password')
    }

    const user = await User.findOne({ email })

    if (!user) {
        throw new CustomError.UnauthenticatedError('Invalid Credentials')
    }

    const isPasswordCorrect = await user.comparePassword(password)

    if (!isPasswordCorrect) {
        throw new CustomError.UnauthenticatedError('Invalid Credentials')

    }

    if (!user.isVerified) {
        throw new CustomError.UnauthenticatedError('Please Verify Your Email ')
    }

    const tokenUSer = createTokenUser(user)
    attachCookiesToResponse({ res, user: tokenUSer })

    res.status(StatusCodes.OK).json({ user: tokenUSer })

}