Form Submission Error Email - despite no obvious error occurring?

Hello! 

We have a promotional pop up that appears after 10 seconds on our home page. 

It seems to be working fine (collecting email address, adding to squarespace built in email list), but we are getting an email with each submission as below: 

Quote

 

Form submission error

You have an unsaved Form Block submission

Your most recent submission to the "bettercup." form on bettercup. didn’t save to your storage method (). This may be the result of a connection issue between your site and your storage service.

 

But we don't have any other storage method set up (see screenshot attached) and the form is capturing the email addresses just fine! 

Does anyone know if there is a form issue here? I don't want to disregard/filter out the error emails in case one day there IS a form error and I miss it. 

Thank you!