Hi David,
The last time you had an issue it was because of SSL. Is your handoff page being forced/redirected to SSL too? Perhaps this is the same issue 1 page later in the flow?
If you could paste your WooCommerce system info, that would give us a little more to work with, too.
Has anything else in your site changed since last time it was working? WooCommerce Update? MyStyle Plugin Update? WordPress Update? Other?
Thanks,
– Sean