Preventing multiple orders on an offer based on email

How can we make sure that only new customers are redeeming our offer on certain funnels? Is there code we could use to check if the email already exists in Funnelish and not let them check out?

It’s impossible without having your own server that collects emails and checks against a secure remote database. there is no other way to do it safely in the client side using JavaScript, unless perhaps a tool like Zapier or similar no-code options might have a solution.

sorry for the delay