Reply To: error in the newsletter form

Hello,

You need to connect it through the API key with your Mailchimp account. Then clear cache and check back.

Or you can read the following articles for help:
https://chimpessentials.com/mailchimp-wordpress/

https://wordpress.org/support/topic/please-provide-a-valid-email-address-get-error-on-mc4wp-form-submission

Regards.
Xtemos Studios.