Hi Alex,
From Method Classic, the Invite emails will show up in the invited users inbox as having come from 'Support@method.me'. Our internal servers here at method utilize Google for Business, a service which is blocked in China, which may be the issue here.
If you could let me know the name of the user, I would be happy to forward to you directly so you can send it to your user!
Thanks Alex.
Regards,
Ben