Sorry to raise this one again. I have read several requests with the similar problem but None of the fixes seem to work for me.
I have the plug in and the module active.
I have selected the correct mailing list (by name not by ID) in the module
I have mailchimp API entered
After all that I am now getting this error
COM_CMC_SUBSCRIBE_FAILED 400: The resource submitted could not be validated. For field-specific details, see the 'errors' array.
Please advise what other information I need to advise