Purchasing multiple items/multi quantity of item in one transaction with android billing library

Question

According to the documentation of Android billing library v4.0+, google has added the ability to purchase multi-quantity of an item.

I enabled the option in Play Console: https://i.stack.imgur.com/OQ6OA.png

But unfortunately the dialog won't allow me to select quantity:

https://i.stack.imgur.com/OQEzA.png

the invoking code looks like this:

        billingClient.querySkuDetailsAsync(params.build(),
                new SkuDetailsResponseListener() {
                    @Override
                    public void onSkuDetailsResponse(BillingResult billingResult,
                                                     List<SkuDetails> skuDetailsList) {
                        Log.d(TAG, "billingDebug: size" + skuDetailsList.size());

                        if (skuDetailsList.size() > 0){
                            BillingFlowParams billingFlowParams = BillingFlowParams.newBuilder()
                                    .setSkuDetails(skuDetailsList.get(0))


                                    .build();
                            String responseCode = billingClient.launchBillingFlow(DetailActivity.this, billingFlowParams).toString();
                            Log.d(TAG, "billingDebug: response: " + responseCode);
                        }



                    }
        });

How can i use the billing library to purchase multiple SKUs / multi quantity of a single SKU? Any help would be appreciated. Thanks in Advance.