cannot resolve method on getstring(java.lang.string)

i'm having a bit of trouble creating an app with 2 factor authentication. I decided to use twilio as my sms gateway and decided to follow along on their tutorial. However I've run into the issue when declaring a url to send out sms's from. For some reason I'm getting an error despite having already declared "mContext"

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import android.content.Context;
import java.io.IOException;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.FormBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

public class MainActivity extends AppCompatActivity {

private EditText mTo;
private EditText mBody;
private Button mSend;
private OkHttpClient mClient = new OkHttpClient();
private Context mContext;

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

mTo = (EditText) findViewById(R.id.txtNumber);
mBody = (EditText) findViewById(R.id.txtMessage);
mSend = (Button) findViewById(R.id.btnSend);
mSend.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        try {

   post(mContext.getString(Integer.parseInt("http://4a61510d.grok.io/sms")), 
 new  
   Callback(){

                @Override
                public void onFailure(Call call, IOException e) {
                    e.printStackTrace();
                }

                @Override
                public void onResponse(Call call, Response response) throws 
   IOException {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            mTo.setText("");
                            mBody.setText("");
                            Toast.makeText(getApplicationContext(),"SMS 
 Sent!",Toast.LENGTH_SHORT).show();
                        }
                    });
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
});
mContext = getApplicationContext();
}
Call post(String url, Callback callback) throws IOException {
RequestBody formBody = new FormBody.Builder()
        .add("To", mTo.getText().toString())
        .add("Body", mBody.getText().toString())
        .build();
Request request = new Request.Builder()
        .url(url)
        .post(formBody)
        .build();
Call response = mClient.newCall(request);
Response.**enqueue**(callback);
return response;
}}

My build.gradle as well

dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', 
{
exclude group: 'com.android.support', module: 'support-annotations'
})
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:25.3.1'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
compile 'com.squareup.okhttp3:okhttp:3.6.0'

and my manifest xml

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

<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>
</application>

this is how i"ve currently changed it with the error still present

post(mContext.getString("http://4a61510d.ngrok.10/sms"), new Callback(){

Try following way

post("http://4a61510d.grok.io/sms", new callback....

Remove mContext.getString() & Integer.parseInt(..) method. As you are not using any resource