It looks like you’ve fixed the issue, as your site isn’t showing the error any longer. When I looked at your site yesterday on my phone, I did see the error, but with thousands of sites running the latest version of Independent Publisher and no one else reporting that error, I’m thinking it was either generated by another plugin introducing a conflict with the theme, or by some modification that you made to the theme.
In any case, it looks like you’re all set now. The site looks great! 🙂