title: Google Pay - ERROR: Request Failed - Unexpected developer error, please try again later
body: <p>When I try to pay(on TEST environment) with Google Pay on a real device I get a the error in the title. </p>
  
  <p>I have tried changing 'gateway' into a string like the google docs show it but so far nothing. </p>
  
  <pre><code>const DETAILS = {
  id: 'COMPANY',
  displayItems: [
    {
      label: 'Phone Bill',
      amount: { currency: 'USD', value: compTotal }
    }
  ],
  total: {
    label: 'COMPANY',
    amount: { currency: 'USD', value: compTotal }
  }
  };
  
  // GOOGLE PAY
  const METHOD_DATA = [{
    supportedMethods: ['android-pay'],
    data: {
      supportedNetworks: ['visa', 'mastercard', 'amex'],
      currencyCode: 'USD',
      environment: 'TEST', // defaults to production
      paymentMethodTokenizationParameters: {
        tokenizationType: 'GATEWAY_TOKEN',
        parameters: {
          gateway: 'braintree',
          'braintree:tokenizationKey': 'sandbox_XXXXXXXXXXX'
        }
      }
    }
  }];
  
  const paymentRequest = new PaymentRequest(METHOD_DATA, DETAILS);
  
  paymentRequest.show()
  .then(paymentResponse =&gt; {
    const { getPaymentToken } = paymentResponse.details;
  
    return getPaymentToken()
      .then(paymentToken =&gt; {
        const { ephemeralPublicKey, encryptedMessage, tag } = paymentToken.details;
  
        return fetch('...', {
          method: 'POST',
          body: {
            ephemeralPublicKey,
            encryptedMessage,
            tag
          }
        })
        .then(res =&gt; res.json())
        .then(paymentResponse.complete('success'), handleConfirm())
        .catch(paymentResponse.complete('fail'), alert(1));
      });
  });
  };
  </code></pre>
  
  <p>Expected result would be the payment going through.</p>