Link to Checkout Instructions yield 403 error

[mnardell]

The link to Checkout Instructions is giving me a 403 error:

403 Forbidden
Code: AccessDenied
Message: Access Denied
RequestId: ZA46WWGQAGFBHZBZ
HostId: PjvlFDc5qO8ECisn+3wJeufnInluL8KKvqguwIiYYJFNOh2yPOBxMh+5tZQoiqZMQbKnbd8xpro=

An Error Occurred While Attempting to Retrieve a Custom Error Document
Code: AccessDenied
Message: Access Denied

The link appears two times in the document as
<a href="{{ site.training_site }}/checkout/">Checkout Instructions</a>
which resolves to:
https://preview.carpentries.org/instructor-training/index.html/checkout/
... the link that works for me is:
https://preview.carpentries.org/instructor-training/instructor/checkout.html