Hi there @tads,

Welcome to the Community! I understand you are trying to work with customizing the error message within signup forms and hope to provide some info regarding it.

At this time, our signup forms are not able to support customization. We are planning to offer more control over the error messaging through a future update. I am going to let our product development team know that is something you would like to have. Additionally, the input fields are only able to support text at this time. I can also pass this along to our product team as a possible update in the future.
While we plan to continue adding features to our in-app forms they are built to be light-weight to allow for fast remote loading when your page loads. If you want to have complete control over the form experience I would recommend building a custom-coded form. This does require some HTML/CSS knowledge, but also provides total control over the experience. This would require installing the complete code for the form on your site which would let the forms load faster and provide control over every aspect. Given the custom nature of those forms our support and community teams are unable to help build/troubleshoot them. You would have to work with a developer or reach out to one of our approved partners for assistance with those. However, we do provide some basis resources around getting started with those forms that you can find in our help center here.

I apologize for any inconvenience this causes for you.

Alex