Why doesnt the onProductPurchased callback get called unless I click it again after the transaction?

Question

The way I see it is that the onProductPurchased method should invoke when a purchase was successful, however that is not the case for me.

It doesn't actually fire unless I complete a purchase and then click the "Purchase" button again. That's when it says Already purchased and I've looked around for a good 3 hours trying to find a solution, yet I can't, I found a SO post explaining a solution to someone who had a similar problem so I tried implementing both the 1st and the 2nd solution but it didn't work, it had the same behaviour.

The SO post I am referring to, please don't mark this as a duplicate, I already tried implementing it and it yielded the same result.

Am I missing some parts of the implementation? I looked at the sample app and it looks fairly similar.

package com.the.name.ui;

import android.content.Intent;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import com.anjlab.android.iab.v3.BillingProcessor;
import com.anjlab.android.iab.v3.TransactionDetails;
import com.the.name.R;

public class PremiumFragment extends Fragment implements BillingProcessor.IBillingHandler {


    private String LICENSE_KEY = "removedforthesakeofthepost";

    BillingProcessor bp;

    private Button btnPurchase;

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

        bp = new BillingProcessor(getContext(), LICENSE_KEY, PremiumFragment.this);
        bp.initialize();


        View rootView = inflater.inflate(R.layout.fragment_premium, container, false);

        btnPurchase = rootView.findViewById(R.id.purchasebtn);

        btnPurchase.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                bp.purchase(getActivity(), "android.test.purchased", null /*or developer payload*/, null);

            }
        });

        return rootView;
    }



    @Override
    public void onProductPurchased(String productId, TransactionDetails details) {
        /*
         * Called when requested PRODUCT ID was successfully purchased
         */

        Toast.makeText(getContext(), "Already purchased", Toast.LENGTH_SHORT).show();

    }

    @Override
    public void onPurchaseHistoryRestored() {

    }

    @Override
    public void onBillingError(int errorCode, Throwable error) {

    }

    @Override
    public void onBillingInitialized() {

    }


    @Override
    public void onDestroy() {
        if (bp != null) {
            bp.release();
            Toast.makeText(getActivity(), "onDestroy", Toast.LENGTH_SHORT).show();
        }
        super.onDestroy();
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (!bp.handleActivityResult(requestCode, resultCode, data))
            super.onActivityResult(requestCode, resultCode, data);
    }

}