As part of this they have locked down certain services (e.g. email verification). Thus you cannot create new Casio IDs, which explains this Reddit thread:
https://www.reddit.com/r/casio/comments/1fwg9v2/casio_id_email_not_coming_through/
That's a problem if you recently bought a new watch that has any Bluetooth syncing capability and did not already have a Casio ID because the official Casio app requires you to login before usage.
You might be able to use a third party app like "G-Shock Smart Sync" (Ivo Zivkov) which doesn't require login.