Why do users see the error "Unrecognized request URL (GET: /v1/tokens.)" after trying to register for an event?

If a user sees the following error after attempting to register for an event, and your organization is using Stripe...

Payment Error: Unrecognized request URL (GET: /v1/tokens.). If you are trying to list objects, remove the trailing slash. If you are trying to retrieve an object, make sure you passed a valid (non-empty) identifier in your code. Please see http://stripe.com/docs or we can help at https://support.stripe.com/.

...it can typically be resolved in the following ways.

1) Ensure that the proper HTTPS secure domain is being used to visit the page.  For example, instead of using http://prefix.nonprofitsoapbox.com/my-event, make sure to always use the secure https://prefix.secure.nonprofitsoapbox.com/my-event.