Hi Harish, Thanks for the reply.
After adding the new API key, I am seeing the list details correctly. The place I am seeing the error is in the log file (MC4WP -> Other -> Debug log) in the POST log:
POST https://us10.api.mailchimp.com/3.0/lists/6fca890fd2/members
That list ID starting with 6fa**** is my old list ID at MC, and I can’t flush it out for some reason.
