I have mail chimp with auto chimp set up on my website. But the Manual sync of all members between my website and Mailchimp comes up with an error 'The Sync Encountered and unknown problem' New members are auto added to a mail chimp mailing list. So no problem there. But I cannot sync over existing 13k members.
Mailchimp support suggested I change the API key, which I did, but I still have the same problem.
Any help appreciated. Alternative is to export via CSV.
Thanks in advance