Invalid email error message

Sent my first MailPoet email out today – worked like a charm, but I do have a problem with my subscription form.
People trying to subscribe to my newsletter are getting an error message telling them their email is invalid. ” Invalid Email Address – Sorry but the email address supplied was invalid and needs to be fixed before you can subscribe to this list. Click here to go back to the form and make the required changes.”
I have tested with several of my own emails and also get the error message.
Subscription page is: https://metroworks.com.au/services/subscribe/

I can send a screenshot of the error message if that helps.

https://www.ads-software.com/plugins/wysija-newsletters/