title: Braintree API: Cannot determine payment method for sandbox transactions
body: <p>I'm currently testing Braintree API with sandbox. When I post nonce to server I get the messages from Braintree API: Amount is required. Cannot determine payment method. 
  I found out that I can use hard coded value for nonce: paymentMethodNonce: "fake-valid-nonce" and in this case I can see the transaction in sandbox. But I would like to see the credit card that I entered in drop-in UI. What might be the cause of "Cannot determine payment method" message?
  My server-side node.js code is the following:</p>
  
  <pre><code>  var amount = req.body.amount;
    // Use the payment method nonce here
    var nonceFromTheClient = req.body.paymentMethodNonce;
  
    var newTransaction = gateway.transaction.sale({
                        amount: amount,                      
                        //paymentMethodNonce: "fake-valid-nonce",
  
                        paymentMethodNonce: nonceFromTheClient,
                        options: {                          
                        submitForSettlement: true }
                        }, function(error, result) {
                        if (result) {
                            res.send(result);
                        } else {                               
                            res.status(500).send(error);
                        }
                     });  
  </code></pre>
  
  <p>My client side code in Swift:</p>
  
  <pre><code>func sendRequestPaymentToServer(nonce: String, amount: String) {
  
      let paymentURL = URL(string: "http://localhost:5000/checkout")!
      var request = URLRequest(url: paymentURL)
      request.httpBody = "paymentMethodNonce=\(nonce)&amp;amount=\(amount)".data(using: String.Encoding.utf8)
      request.httpMethod = "POST"
  
      URLSession.shared.dataTask(with: request) { (data, response, error) -&gt; Void in
          guard let data = data else {
              print(error!.localizedDescription)
              return
          }
          if let result = try? JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] {
              if result?["success"] as? Bool == true {
                  print("Successfully charged. Thanks So Much :)")
              }
              else if let message = result?["message"] {
                  print(message)
              }
              //dump(result)
          } else {
              print("No json result.")
          }
          }.resume()
  }
  </code></pre>