def widgets_url
      sandbox = preferred_test_mode ? '/sandbox' : ''
      {
        'us' => "https://static-na.payments-amazon.com/OffAmazonPayments/us#{sandbox}/js/Widgets.js",
        'uk' => "https://static-eu.payments-amazon.com/OffAmazonPayments/uk#{sandbox}/lpa/js/Widgets.js",