Mailchimp error: Resource Not Found - The requested resources could not be found.

Veyr new to all this technology so need some hand holding here. I’m hung up on ‘Tag’ when adding a new subscriber to MailChimp. I’m not sure what’s needed to be included there. I only want 3 pieces of information from my subscribers - First Name, Last Name and Email. That’s what I included in ‘Tag’ (see attached) but when I went to run my test, I recevied an error message (see attached). Any guidance would be greatly appreciated!