Hustle issue when using already registered email in Mailchimp

I’m getting an error message in Hustle when filling a slide-in:

“Something went wrong. Please try again.”

I noticed that the error pops when it’s an email address in the database already – a duplicate. It looks like it only occurs when this happens, not a plugin conflict. I don’t know if the error messages can me customixzed, would it be possible so I can inform the member that the email is already registered in this case?