how to make button stop working once timer is over

Question

i have created a 50 second timer. Once the timer reach zero a pop view will appear displaying the score and the button on the application should stop working but i am not sure how to make the button stop being clickable

 equal.setOnClickListener{
            ++total
            if(ans == ans4 || ans1 == ans4 || ans2 == ans4 || ans3 == ans4 || ans == ans5 || ans1 == ans5 || ans2 == ans5 || ans3 == ans5
                || ans == ans6 || ans1 == ans6 || ans2 == ans6 || ans3 == ans6){
                answer.setText("Correct")
                answer.setTextColor(Color.GREEN)
                ++correct
                score.setText("Score: $correct/$total")
            } else {
                answer.setText("Wrong")
                answer.setTextColor(Color.RED)
                score.setText("Score: $correct/$total")
            }
}

val timer = object: CountDownTimer(50000, 1000) {
            override fun onTick(millisUntilFinished: Long) {
                countTimer.setText("Remaining: " + millisUntilFinished / 1000);

                if (correct >= 5){
                    countTimer.setText("Remaining: " + (millisUntilFinished + 10000  ) / 1000);
                }
            }

            override fun onFinish() {
                popup()
            }
        }
        timer.start()
    }

fun popup(){
        var popupView: View = layoutInflater.inflate(R.layout.score, null)
        var gameover_textView  = popupView.findViewById<TextView>(R.id.endMessage)
        gameover_textView.setText("Score: $correct/$total ")
        var popupwindow = PopupWindow(this)
        popupwindow.contentView = popupView
        popupwindow.showAtLocation(popupView, Gravity.CENTER, 0, 100)

        popupView.setOnClickListener{
            popupwindow.dismiss()
        }
    }

Answer 1

equal.setClickable(false);
equal.setClickable(true);
//according to the requirement