S2member integration to Mail chimp

I have set up the Mail Chimp integration and my registration page shows a tick box with the ‘Yes, I want to receive updates via email.’ message.

When a new user Registers (as Free Subscriber) the registration works well, including sending password email, but no information is recorded in MailChimp.

I only have |EMAIL| and |FNAME| as ‘required’ in the Mail Chimp settings.

Any clues welcome please