Can’t connect with Mailchimp, getting a 400 Invalid resource error

Hi, hope you can help with this. No matter what I do, I get a 400 Invalid Resource response with the following code

[{"field":"email_address","message":"This value should not be blank."}]

of course I double checked and email address is not blank (otherwise the form wouldn’t even go through). I also get the email address in Google Tag Manager Data Layer and I can export to Google Sheets automatically, so it seems to be related to this plugin or Mailchimp.

Any idea on how to solve please?

Thank you in advance!

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