How can I replace fragment inside a fragment?

I have an Activity with a ViewPager, each page of the ViewPager has a Fragment.

Inside my Screen3Fragment I have a LinearLayout (lly_fragments) where I am showing some other fragments. I start by showing the fragment Screen3_1

public class Screen3Fragment extends Fragment {

    private FragmentManager manager;
    private FragmentTransaction transaction;


    public static Screen3Fragment newInstance() {
        final Screen3Fragment mf = new Screen3Fragment();
        return mf;
    }

    public Screen3Fragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_screen3, container, false);
        Screen3_1Fragment frag31 = new Screen3_1Fragment();
        manager = getChildFragmentManager();
        transaction = manager.beginTransaction();
        transaction.add(R.id.lly_fragments,frag31,"frag31");
        transaction.addToBackStack("frag31");
        transaction.commit();
        return v;
    }

}

This works fine without problems. Problem comes when, from within frag31 (which is inside Screen3Fragment), I want to call fragt32, for that I do the following.

public class Screen3_1Fragment extends Fragment {

    private ImageButton imgbt_timer;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_screen3_1,container,false);
        imgbt_timer = (ImageButton) v.findViewById(R.id.bT_scr31_timer);
        imgbt_timer.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getChildFragmentManager().beginTransaction()
                                            .replace(R.id.lly_fragments, new Screen3_2Fragment(), "frag32")
                                            .commit();
            }
        });


        return v;
    }
}

As I read in other answers, the line transaction.replaceshould do the trick and replace the existing frag31 by the given frag32 inside the same given container lly_fragments.

However, I get java.lang.IllegalArgumentException: No view found for id..... I am not sure why.