Hi ​@rs0865, 

Unfortunately, as far as I know, you can’t add additional fields into the default modal implementation. I’m hoping someone knows a hack or some undocumented way to do this!

The only way that I know to do this is would require you to use the Klaviyo API for Back In Stock if you have technical resources, you’re effectively building your own way to add people to the waitlist.   But again, this isn’t trivial to do.

One potential work around is in the Back in Stock Flow, you can send a confirmation email where you can ask them to click on a link to sign up or update/manage their preferences.  One technique I’ve tried is to ask them “Don’t want to miss the back in stock email?  Make sure you subscribe to SMS!” - then that can lead to an embedded multi-step Signup Form where you can ask for their name, and SMS optin.  Just make sure your Back in Stock Flow also sends an SMS for those that are opted in!