You can always update the http:// to https:// manually in order to continue with the checkout process.
That url must be wrong or maybe only viewable locally for you. Is the https certificate installed and functioning properly on that test site? We just installed a cirtificate on our dev server to better test that it redirects properly, so we'll make sure to get it adjusted, but it would be helpful if you tested the rest of the process so we could incorporate any other suggestions you might have.