Force close when try to Invoke method

1 - Make sure to add Internet permission to your AndroidManifest.xml file:

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

Note: uses-permission goes before application tag. i.e:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.awsapigatwway">
    <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>
</manifest>

2 - Make sure to execute your API Gateway call within an ASyncTask

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    new AsyncTask<Void, Void, Void>() {
        @Override
        protected Void doInBackground(Void... params) {
            ApiClientFactory factory = new ApiClientFactory();

            final PetStoreClient client = factory.build(PetStoreClient.class);

            Pet pet = client.petsPetIdGet("1");

            Log.d(pet.getType(), String.valueOf(pet.getPrice()));

            return null;
        }
    }.execute();
}

In this case, response should be seen on Logcat Debug.