Sending email verification via smtp by kotlin

I tried to make a validation code when user sign up via below fun

class GMailSender : Authenticator() {


val fromEmail = "myemail@a.com"
val password = "mypwd"


val code = (1000..9999).random().toString()



override fun getPasswordAuthentication(): PasswordAuthentication {
    return PasswordAuthentication(fromEmail, password)
}


fun sendEmail(toEmail: String){

    CoroutineScope(Dispatchers.IO).launch {
        val props = Properties()




        props.setProperty("mail.transport.protocol", "smtp")
        props.setProperty("mail.host", "smtp.gmail.com")
        props.put("mail.smtp.auth", "true")
        props.put("mail.smtp.port", "465")
        props.put("mail.smtp.socketFactory.port", "465")
        props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory")
        props.put("mail.smtp.socketFactory.fallback", "false")
        props.put("mail.smtp.ssl.enable", "true")
        props.setProperty("mail.smtp.quitwait", "false")

        val session = Session.getDefaultInstance(props, this@GMailSender)



        val message = MimeMessage(session)
        message.sender = InternetAddress(fromEmail)                                
        message.addRecipient(Message.RecipientType.TO, InternetAddress(toEmail))    
        message.subject =
            "verfication code"                                              
        message.setText("validation" + code)                                               


        Transport.send(message)


    }

}

and it really works. but the problem is when i tried to compare by below code

 private fun check_VerificationCode(): Boolean {
    var check = false
    binding.verificationBtn.setOnClickListener {
        if (binding.verificationArea.text.toString() == GMailSender().code ) {
            check = true
        } else {
            Toast.makeText(this, "unmatch", Toast.LENGTH_SHORT).show()              Toast.makeText(this,binding.verificationArea.text.toString(),Toast.LENGTH_SHORT).show()
            Toast.makeText(this,GMailSender().code,Toast.LENGTH_SHORT).show()
        }
    }
    return check
}

}

and i have two problems.

1. The number in the email(the number that is created when email send) is different from the actual numbers(GMailSender().code)
2. The random number is keep changing.

How can i match them correctly?