import com.alipay.AlipayPackage;  // <--- import
 public class MainActivity extends Activity implements DefaultHardwareBackBtnHandler {
    ...
    private AlipayPackage alipay;
    ...
    protected void onCreate(Bundle savedInstanceState) {
      ...
      alipay = new AlipayPackage(this);
      ...
      mReactInstanceManager = ReactInstanceManager.builder()
        ...
        .addPackage(alipay)
      }  
    ...
  }