title: Stripe API returns no source although there are some according to dashboard
body: <p>My stripe account is in test mode.</p>
  
  <p>I request all sources (with cards) for a given customer using:</p>
  
  <pre><code>curl "https://api.stripe.com/v1/customers/cus_FWzlniSobJD2yO/sources" \
      -u sk_test_SECRET_KEY: \
      -G
  </code></pre>
  
  <p>I get the following response:</p>
  
  <pre><code>{
    "object": "list",
    "data": [
  
    ],
    "has_more": false,
    "url": "/v1/customers/cus_FWzlniSobJD2yO/sources"
  }
  </code></pre>
  
  <p>You can see that 'data', that should contain the customer's payment sources, is empty.</p>
  
  <p>The cards have been saved from the front with stripe.js using:</p>
  
  <pre><code>stripe.handleCardPayment(intentClientSecret, cardElement, {
      payment_method_data: {
          billing_details: {name: 'Firstname Lastname'}
      },
      save_payment_method: true
  });
  </code></pre>
  
  <p>Cards appearing in customer's details in my dashboard:
  <a href="https://i.stack.imgur.com/L05Qw.png" rel="noreferrer"><img src="https://i.stack.imgur.com/L05Qw.png" alt="Cards appearing in customer details"></a></p>