Hi @EBloom,
When you refer to contact ID, are you referring to the object ID in the CRM? I don’t believe that id is generated until the form is submitted so I don’t think there’s anything you can pass through until the thank you page maybe there’s a conversion snippet you can pass but even then i think there’s a slight delay upon submission and record creation. I think the thread @BérangèreL linked above from Teun’s solution might be the better route since you’ll be passing the email directly from the input as the form is being submitted.