Newsletter sign up button not working

I’ve used the plugin on my blog with Mailchimp but once an email address is entered and the submit button is pressed, the subscriber doesn’t get added to the mailchimp list (nor was an email being sent to the subscriber with the opt in option). I’ve tested this with my own email addresses and it doesn’t work. I’ve entered all of the mailchimp details correctly so I’m totally confused. My site is https://muminbrum.com please can you take a look. Thanks

https://www.ads-software.com/plugins/newsletter-sign-up/