<uses-permission android:name="android.permission.INTERNET" />

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <!--EditText text to enter amount-->
    <EditText
        android:id="@+id/idEdtAmount"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layout_margin="20dp"
        android:hint="Enter amount to be payed"
        android:inputType="number" />

    <!--button to make payment-->
    <Button
        android:id="@+id/idBtnPay"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/idEdtAmount"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp"
        android:text="Pay using RazorPay"
        android:textAllCaps="false" />

</RelativeLayout>

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import com.razorpay.Checkout;
import com.razorpay.PaymentResultListener;

import org.json.JSONException;
import org.json.JSONObject;

public class MainActivity extends AppCompatActivity implements PaymentResultListener {

    // variables for our 
    // edit text and button.
    private EditText amountEdt;
    private Button payBtn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // initializing all our variables.
        amountEdt = findViewById(R.id.idEdtAmount);
        payBtn = findViewById(R.id.idBtnPay);

        // adding on click listener to our button.
        payBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // on below line we are getting 
                // amount that is entered by user.
                String samount = amountEdt.getText().toString();

                // rounding off the amount.
                int amount = Math.round(Float.parseFloat(samount) * 100);

                // initialize Razorpay account.
                Checkout checkout = new Checkout();

                // set your id as below
                checkout.setKeyID("Enter your key id here");

                // set image
                checkout.setImage(R.drawable.gfgimage);

                // initialize json object
                JSONObject object = new JSONObject();
                try {
                    // to put name
                    object.put("name", "Geeks for Geeks");

                    // put description
                    object.put("description", "Test payment");

                    // to set theme color
                    object.put("theme.color", "");

                    // put the currency
                    object.put("currency", "INR");

                    // put amount
                    object.put("amount", amount);

                    // put mobile number
                    object.put("prefill.contact", "9284064503");

                    // put email
                    object.put("prefill.email", "chaitanyamunje@gmail.com");

                    // open razorpay to checkout activity
                    checkout.open(MainActivity.this, object);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    @Override
    public void onPaymentSuccess(String s) {
        // this method is called on payment success.
        Toast.makeText(this, "Payment is successful : " + s, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onPaymentError(int i, String s) {
        // on payment failed.
        Toast.makeText(this, "Payment Failed due to error : " + s, Toast.LENGTH_SHORT).show();
    }
}