Ahh. That explains it.
Regular live production sites have a "/method/" URL.
The new, up and coming, optional site is the "stage" site, at a "/stage/" URL.
You are using the /stage/ site URL in the login. Your customers should always be given a /method/ URL.
The stage site is not always guaranteed to be up. i.e. if only a February version is available, only the regular live site will be available at /method/. But if we are staging the March version, /stage/ would become available again.
I think we need to do something smarter on our end if someone has a hardcode stage link, such as automatically redirect if the /stage/ site is unavailable to the always present /method/ site.
I hope that makes sense - I know having two simultaeous versions of Method can be confusing!
Paul