private static final String CONFIG_ENVIRONMENT = PayPalConfiguration.ENVIRONMENT_NO_NETWORK;

    // note that these credentials will differ between live & sandbox environments.
    private static final String CONFIG_CLIENT_ID = "credentials from developer.paypal.com";

    private static final int REQUEST_CODE_PAYMENT = 1;
    private static final int REQUEST_CODE_FUTURE_PAYMENT = 2;
    private static final int REQUEST_CODE_PROFILE_SHARING = 3;

    private static PayPalConfiguration config = new PayPalConfiguration()
            .environment(CONFIG_ENVIRONMENT)
            .clientId(CONFIG_CLIENT_ID)
            // The following are only used in PayPalFuturePaymentActivity.
            .merchantName("Example Merchant")
            .merchantPrivacyPolicyUri(Uri.parse("https://www.example.com/privacy"))
            .merchantUserAgreementUri(Uri.parse("https://www.example.com/legal"));

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Intent intent = new Intent(this, PayPalService.class);
        intent.putExtra(PayPalService.EXTRA_PAYPAL_CONFIGURATION, config);
        startService(intent);
    }

    public void onBuyPressed(View pressed) {
        /*
         * PAYMENT_INTENT_SALE will cause the payment to complete immediately.
         * Change PAYMENT_INTENT_SALE to
         *   - PAYMENT_INTENT_AUTHORIZE to only authorize payment and capture funds later.
         *   - PAYMENT_INTENT_ORDER to create a payment for authorization and capture
         *     later via calls from your server.
         *
         * Also, to include additional payment details and an item list, see getStuffToBuy() below.
         */
        PayPalPayment thingToBuy = getThingToBuy(PayPalPayment.PAYMENT_INTENT_SALE);

        /*
         * See getStuffToBuy(..) for examples of some available payment options.
         */

        Intent intent = new Intent(SampleActivity.this, PaymentActivity.class);

        // send the same configuration for restart resiliency
        intent.putExtra(PayPalService.EXTRA_PAYPAL_CONFIGURATION, config);

        intent.putExtra(PaymentActivity.EXTRA_PAYMENT, thingToBuy);

        startActivityForResult(intent, REQUEST_CODE_PAYMENT);
    }

    private PayPalPayment getThingToBuy(String paymentIntent) {
        return new PayPalPayment(new BigDecimal("0.01"), "USD", "sample item",
                paymentIntent);
    }