UX issue with Post Code (aka Zip)

When a user works through an Event Registration form, they come to the payment details and the Stripe.js generated box prompts for Card Number, MM / YY and CVC

But then the Postcode is also added as an extra field which is not always obvious

They then continue through the payment form, including entering their full Billing address

When they 'Submit', an error message appears "Your postal code is incomplete". The screen focus jumps to the Billing Address where the user can see their Postcode! However, the post code is needed higher up the screen, which is not at all obvious.

You can test this behaviour on my site here: https://breinton.com/component/civicrm/?task=civicrm/event/register&reset=1&id=130