In-app Billing Initalise

MainActivity.java

BillingClient mBillingClient;

mBillingClient = BillingClient.newBuilder(this).setListener(new PurchasesUpdatedListener() {
    @Override
    public void onPurchasesUpdated(int responseCode, @Nullable List<Purchase> purchases) {
        for(Purchase purchase: purchases) {
            //When every a new purchase is made
        }
    }
}).build();

mBillingClient.startConnection(new BillingClientStateListener() {
    @Override
    public void onBillingSetupFinished(@BillingClient.BillingResponse int billingResponseCode) {
        if (billingResponseCode == BillingClient.BillingResponse.OK) {
            // The billing client is ready. You can query purchases here.
        }
    }
    @Override
    public void onBillingServiceDisconnected() {
        // Try to restart the connection on the next request to
        // Google Play by calling the startConnection() method.
    }
});

I am newbie, I am trying to integrate in-app subscription last two day. I have done with another lib and test it by uploading apk on Alpha testing. My payment was successful but with that lib i am getting 102 error. so i am trying to implement in-app subscription using this lib but not getting idea that how to make request for subscription and how to check that my subscription is activated or not. And if subscription is successfully activated then how to check that user has cancelled subscription or not for second time when user start the app? Please do some help, i would be very appreciative.

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