title: Braintree - Android SDK: existing card verification by just passing CVV for processing payment
body: <p>I have integrated Braintree Android SDK in studio for payment process. Instead of using Drop-in UI I am using my customised UI which has 3 tabs - Saved Cards, New Card and Cash. In Saved card - the list of saved cards is displayed while in New card - user is prompt to enter Card no, expiration date and CVV and the option to save the card details and for payment through cash - cash tab is used, card details are not saved in front / back end everything is working fine. But my requirement is - if user selects existing card for payment then my application wants to prompt user to enter CVV of the existing card for authorization. </p>
  
  <p>I am using CardBuilder.java to build card details for newly entered card which is, </p>
  
  <pre><code>CardBuilder cardBuilder = new CardBuilder()
      .cardNumber(mEdtCardNumber.getText().toString())
      .expirationDate(mEdtExpirationYear.getText().toString())
      .cvv(mEdtCvv.getText().toString());
  
  Card.tokenize(mBraintreeFragment, cardBuilder);
  </code></pre>
  
  <p>and am getting nounce in <code>onPaymentMethodNonceCreated</code>.</p>
  
  <p>And for existing card after entering CVV am using same process like,</p>
  
  <pre><code>CardBuilder cardBuilder = new CardBuilder().cvv(entered CVV);
  Card.tokenize(mBraintreeFragment, cardBuilder);
  </code></pre>
  
  <p>but my <code>onPaymentMethodNonceCreated</code> is not getting called and instead onError is called and the error is,</p>
  
  <pre><code>{"error":{"message":“Credit card is invalid”},
  “fieldErrors”:[{"field":“creditCard”,
  “fieldErrors”:[{"field":“expirationDate”,“code”:“81709”,“message”:“Expiration date is required”},
  {"field":“number”,“code”:“81714”,“message”:“Credit card number is required”},
  {"field":“base”,“code”:“81725”,“message”:“Credit card must include number, payment_method_nonce, or venmo_sdk_payment_method_code”}]}]}
  </code></pre>
  
  <p>But the same thing is working in iOS client SDK.</p>
  
  <p>So my concern is, it is the right way to validate existing card or there is another way. Braintree - Drop In UI doesn't ask for CVV on existing card payment and I am also not getting any code in their API. I have gone through whole API and counld't find any such thing.</p>
  
  <p>Where as, the backend PHP is used to make payment method calls, from front end I am just passing the nounce.</p>
  
  <p>Can anyone please help me how to validate existing card by CVV?</p>