private IabHelper mHelper;
private IabBroadcastReceiver mBroadcastReceiver;
private IabHelper.QueryInventoryFinishedListener mGotInventoryListener;
boolean mIsPremium = false;
static final String SKU_PREMIUM = "premium";
static final int RC_REQUEST = 10001;
private IabHelper.OnIabPurchaseFinishedListener mPurchaseFinishedListener;

String base64EncodedPublicKey = "TU_CLAVE_APP"
mHelper = new IabHelper(this, base64EncodedPublicKey);

mHelper.enableDebugLogging(true); //quitarlo si es modo release

Log.d(TAG, "Starting setup.");
    mHelper.startSetup(new IabHelper.OnIabSetupFinishedListener() {
        @Override
        public void onIabSetupFinished(IabResult result) {
            Log.d(TAG, "Setup finished.");

            if (!result.isSuccess()) {
                Log.e(TAG, "In-app Billing setup failed: " + result);
            } else {
                Log.d(TAG, "In-app Billing is set up OK");
            }

            if (mHelper == null) return;

            mBroadcastReceiver = new IabBroadcastReceiver((IabBroadcastReceiver.IabBroadcastListener) MainActivity.this);
            IntentFilter broadcastFilter = new IntentFilter(IabBroadcastReceiver.ACTION);
            registerReceiver(mBroadcastReceiver, broadcastFilter);

            // IAB is fully set up. Now, let's get an inventory of stuff we own.
            Log.d(TAG, "Setup successful. Querying inventory.");
            try {
                mHelper.queryInventoryAsync(mGotInventoryListener);
            } catch (IabHelper.IabAsyncInProgressException e) {
                complain("Error querying inventory. Another async operation in progress.");
            }
        }
    });

mGotInventoryListener = new IabHelper.QueryInventoryFinishedListener() {
        public void onQueryInventoryFinished(IabResult result, Inventory inventory) {
            Log.d(TAG, "Query inventory finished.");

            // Have we been disposed of in the meantime? If so, quit.
            if (mHelper == null) return;

            // Is it a failure?
            if (result.isFailure()) {
                complain("Failed to query inventory: " + result);
                return;
            }

            Log.d(TAG, "QUERY inventory was successful.");


            // Do we have the premium upgrade?
            Purchase premiumPurchase = inventory.getPurchase(SKU_PREMIUM);
            mIsPremium = (premiumPurchase != null && verifyDeveloperPayload(premiumPurchase));
            Log.d("PREMIUM =","User is " + (mIsPremium ? "PREMIUM" : "NOT PREMIUM"));
            alert("User is " + (mIsPremium ? "PREMIUM" : "NOT PREMIUM"));

            Log.d(TAG, "Initial inventory query finished; enabling main UI.");
        }
    };

String payload = "mypurchasetoken";

try {
    mHelper.launchPurchaseFlow(MainActivity.this, SKU_PREMIUM, RC_REQUEST,
            mPurchaseFinishedListener, payload);
} catch (IabHelper.IabAsyncInProgressException e) {
    e.printStackTrace();
}

mPurchaseFinishedListener = new IabHelper.OnIabPurchaseFinishedListener() {
    public void onIabPurchaseFinished(IabResult result, Purchase purchase) {
        Log.d(TAG, "Purchase finished: " + result + ", purchase: " + purchase);

        // if we were disposed of in the meantime, quit.
        if (mHelper == null) return;

        if (result.isFailure()) {
            complain("Error purchasing: " + result);
            return;
        }
        if (!verifyDeveloperPayload(purchase)) {
            complain("Error purchasing. Authenticity verification failed.");
            return;
        }

        Log.w(TAG, "Purchase successful.");

        if (purchase.getSku().equals(SKU_PREMIUM)) {
            // bought the premium upgrade!
            Log.w(TAG, "Purchase is premium upgrade. Congratulating user.");
            alert("Thank you for upgrading to premium!");
            mIsPremium = true;
        }
    }
};