Use stripe-3ds2-base-branch as the base branch. See that in https://github.com/3scale/porta/blob/f1143d19f4664285fe5e5855774bb7c59e516365/app/views/payment_gateways/_stripe_elements.html.erb#L130 the country code is hardcoded. This is because we use to make the clients enter a country name and that was compatible with stripe before, but this new API endpoint only allows countries as ISO 3166-1 alpha-2 codes.

So I hardcoded 'ES' to bypass this error message:

But of course, we must fix the problem for real instead of ignoring it like that.

To test it locally, besides following the instructions in the PDF in the Epic, first make sure that you have the rolling update stripe_elements: true or add it yourself in your config/rolling_updates.yml