not assignable to 'android.app.activity' e

I am implementing Adobe Creative SDK. I am getting the following error in in my my manifest file:

'com.example.nick.avierytest2.MainActivity is not assignable to android.app.activity'

This is my XML file:

<?xml version="1.0" encoding="utf-8"?>

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

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

This is my main activity class:

public class MainActivity extends Application implements IAdobeAuthClientCredentials {

/* Be sure to fill in the two strings below. */
private static final String CREATIVE_SDK_CLIENT_ID = "";
private static final String CREATIVE_SDK_CLIENT_SECRET = "";

@Override
public void onCreate() {
    super.onCreate();
    AdobeCSDKFoundation.initializeCSDKFoundation(
            getApplicationContext(),
            AdobeAuthIMSEnvironment.AdobeAuthIMSEnvironmentProductionUS
    );
}

@Override
public String getClientID() {
    return CREATIVE_SDK_CLIENT_ID;
}

@Override
public String getClientSecret() {
    return CREATIVE_SDK_CLIENT_SECRET;
}

}

Every other time I have seen this question on stackoverflow it was someone trying to declare a fragment in the manifest but that is not the problem here and I have not been able to find the solution.

Thank you for your help.

MainActivity extends Application

Of course an Application is not assignable to an Activity.

Either change this to MainActivity extends Activity, or move the android:name=".MainActivity" reference in the manifest to the application tag (and remove that activity). In the latter case also consider renaming the class from MainActivity to e.g. MyApplication.