title: Integration of braintree causing issues
body: <p>I'm working on Braintree for the first time and getting issues in very first step. I'm not able to access dropin functionality and other..
  I need help to sort it out.</p>
  
  <p>I followed steps given here : <a href="https://developers.braintreepayments.com/javascript+php/start/overview" rel="noreferrer">https://developers.braintreepayments.com/javascript+php/start/overview</a></p>
  
  <p>First step is Javascript Client! - I followed as mentioned, added script</p>
  
  <pre><code> &lt;script src="https://js.braintreegateway.com/v2/braintree.js"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>Then added HTML part </p>
  
  <pre><code>&lt;form id="checkout" method="post" action="/checkout"&gt;
    &lt;div id="dropin"&gt;&lt;/div&gt;
    &lt;input type="submit" value="Pay $10"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>And at last I've added below script in script tag.</p>
  
  <pre><code>braintree.setup("CLIENT_TOKEN_KEY", 'dropin', {
     container: 'checkout'
  })
  </code></pre>
  
  <p>I have checked with Client Token Key obtained from our server.</p>
  
  <p>for next step, I added configurations as mentioned</p>
  
  <pre><code>Braintree_Configuration::environment('sandbox');
  Braintree_Configuration::merchantId('use_your_merchant_id'); //updated with our merchant id
  Braintree_Configuration::publicKey('use_your_public_key'); // updated with our public key
  Braintree_Configuration::privateKey('use_your_private_key'); //updated with our private key
  </code></pre>
  
  <p>then added</p>
  
  <pre><code>$clientToken = Braintree_ClientToken::generate(array(
     "customerId" =&gt; $aCustomerId 
  ));
  </code></pre>
  
  <p>Now, <strong>Issues I'm getting</strong> - </p>
  
  <p>When I updated $aCustomerId with our customer id, I got a Fatal Error of "customer_id" field undefined in Braintree_ClientToken. So removed array("customer"=>$aCustomerId) and got the client token..</p>
  
  <p>That client token is used in <code>brantree.setup('TOKEN_KEY','dropin',{container:'checkout'})</code> and got </p>
  
  <pre><code>Error: Unable to find valid container. -braintree.js(line 18) 
  </code></pre>
  
  <p>I also mentioned once <code>var braintree = Braintree.create("CLIENT_TOKEN_KEY");</code> above <code>brantree.setup('TOKEN_KEY','dropin',{container:'checkout'})</code> at that time I've got <code>TypeError: braintree.setup is not a function</code></p>
  
  <p>I'm trying to sort it out this from last two days, but still I didn't get dropin screen as showed in demo.</p>
  
  <p>Hope for good help..</p>