BraintreeKotlin in androidstudio

AndroidManifest.xml
----------------------

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.braintreekotlinsample">

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <application
            android:allowBackup="true"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <activity android:name="com.braintreepayments.api.BraintreeBrowserSwitchActivity"
                  android:launchMode="singleTask">
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <category android:name="android.intent.category.DEFAULT" />
                <category android:name="android.intent.category.BROWSABLE" />
                <data android:scheme="${applicationId}.braintree" />
            </intent-filter>
        </activity>
    </application>

</manifest>

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

    <LinearLayout
            android:id="@+id/waiting_group"
            android:layout_centerInParent="true"
            android:orientation="vertical"
            android:visibility="visible"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Please wait for the token to get"
                android:layout_gravity="center_horizontal"/>


    </LinearLayout>


    <LinearLayout
            android:id="@+id/payment_group"
            android:layout_centerInParent="true"
            android:orientation="vertical"
            android:visibility="gone"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="CHECKOUT"
                android:layout_gravity="center_horizontal"
                android:textStyle="bold"
                android:textSize="20sp"/>
        <android.support.design.widget.TextInputLayout android:layout_width="match_parent"
                                                       android:layout_height="wrap_content">

                <EditText
                        android:id="@+id/edt_payment"
                        android:hint="Choose the amount to pay(USD)"
                        android:gravity="center_horizontal"
                        android:inputType="number"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"/>

        </android.support.design.widget.TextInputLayout>

        <Button
                android:id="@+id/btn_pay"
                android:text="PAY"
                android:layout_gravity="center_horizontal"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"/>


    </LinearLayout>


</RelativeLayout>


-----------------------------------------
MainActivity.kt
-----------------------------------------

package com.example.braintreekotlinsample
import android.app.Activity
import android.app.VoiceInteractor
import android.content.Intent
import android.os.AsyncTask
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.os.Parcel
import android.os.Parcelable
import android.util.Log
import android.view.View
import android.widget.Toast
import com.android.volley.Request
import com.android.volley.RequestQueue
import com.android.volley.Response
import com.android.volley.toolbox.StringRequest
import com.android.volley.toolbox.Volley
import com.braintreepayments.api.dropin.DropInActivity
import com.braintreepayments.api.dropin.DropInRequest
import com.braintreepayments.api.dropin.DropInResult
import com.braintreepayments.api.models.PaymentMethodNonce
import com.loopj.android.http.AsyncHttpClient
import com.loopj.android.http.TextHttpResponseHandler
import cz.msebera.android.httpclient.Header
import kotlinx.android.synthetic.main.activity_main.*
import java.io.File
import kotlin.Exception

class MainActivity : AppCompatActivity() {

    companion object{
        val API_GET_TOKEN = "TOKEN LINK HERE"
        val API_CHECKOUT = "CHECKOUT LINK"
        val REQUEST_CODE: Int = 111

        internal lateinit var token:String
        internal lateinit var amount:String
        internal var paramsHash:HashMap<String,String>?=null

    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

       getToken()


        //Event

        btn_pay.setOnClickListener {
            val dropInRequest = DropInRequest().clientToken(token)
            startActivityForResult(dropInRequest.getIntent(this),REQUEST_CODE)
        }
    }

   private fun getToken(){
       val androidClient = AsyncHttpClient()
       androidClient.get(API_GET_TOKEN, object:TextHttpResponseHandler(){
           override fun onSuccess(statusCode: Int, headers: Array<out Header>?, responseString: String?) {
               runOnUiThread {
                   payment_group.visibility = View.VISIBLE
                   waiting_group.visibility = View.GONE
                   token = responseString!!.toString()
               }
           }

           override fun onFailure(
               statusCode: Int,
               headers: Array<out Header>?,
               responseString: String?,
               throwable: Throwable?
           ) {
                runOnUiThread {
                    Toast.makeText(this@MainActivity,"Failed to load token:"+throwable.toString(),Toast.LENGTH_SHORT).show()

                }
           }

       })
   }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        if(requestCode == REQUEST_CODE){

        }
            if(requestCode == Activity.RESULT_OK){
                val result:DropInResult = data!!.getParcelableExtra<DropInResult>(DropInResult.EXTRA_DROP_IN_RESULT)
                val nonce:PaymentMethodNonce? = result.paymentMethodNonce
                val stringNonce:String = nonce!!.nonce

                if(!edt_payment.text.toString().isEmpty()){
                    amount = edt_payment.text.toString()
                    paramsHash = HashMap()

                    paramsHash!!["amount"] = amount
                    paramsHash!!["nonce"] = stringNonce

                    sendPayment()
                }
                else
                    Toast.makeText(this@MainActivity,"Please enter valid amount",Toast.LENGTH_LONG).show()

            }

        else if(resultCode == Activity.RESULT_CANCELED)
                Toast.makeText(this@MainActivity,"User Cancel",Toast.LENGTH_LONG).show()

        else {
                val error:Exception = data!!.getSerializableExtra(DropInActivity.EXTRA_ERROR) as Exception
                Log.d("ERROR", error.message)

            }


    }

    private fun sendPayment(){
        val queue:RequestQueue = Volley.newRequestQueue(this@MainActivity)

        val stringRequest = object:StringRequest(Request.Method.POST, API_CHECKOUT,
            Response.Listener { response ->
                if(response.toString().contains("Successful"))
                    Toast.makeText(this@MainActivity, "Transaction Successful",Toast.LENGTH_SHORT).show()
                else
                    Toast.makeText(this@MainActivity, "Transaction Failed",Toast.LENGTH_SHORT).show()
            }, Response.ErrorListener { error ->
                Log.d("ERROR","Volley Error"+error.message)

            }){
            override fun getParams(): MutableMap<String, String?>? {
                if(paramsHash == null)
                    return null
                var params = HashMap<String,String?>()
                for(key:String in paramsHash!!.keys)
                    params.set(key,paramsHash!![key])
                return  params



            }

            override fun getHeaders(): MutableMap<String, String> {
                val params = HashMap<String,String>()
                params["Content-Type"] = "application/x-www-form-urlencoded"
                return params
            }
        }
    }


}