Merge event_id into redirect link.

We are using the api and getting a payload whenever a user finishes taking the quiz which is awesome, and inside that payload there is an “event_id” which is awesome! Because if a user fails to enter their name, but makes a purchase after the quiz we can tie their quiz answers to their event_id! 

ONE PROBLEM!! We need to redirect the user to our shop after they finish the quiz, so in the final step we have a redirect which looks something like. 

https://n8n.oursite.com/webhook/getCartUrl_v2?email=@{enter your email}&eventId=@??????

QUESTION - How do you merge the event_id into the redirect link? This is meant to catch quiz answers for the many people who change their email address at checkout breaking the truthiness of email.  

URGENT! - This is a dealbreaker if we cannot find a way to connect these redirects to quiz answers then we will have to find another option.