Using Zoho Subscriptions as payment Wall

Using Zoho Subscriptions as payment Wall

I am looking to use Zoho Subscriptions as payment wall in my Zoho creator application.

The Zoho Creator will be given a set number of free events and once the limit is reached they will be presented with a Zoho Subscription Sign Up Form.

The challenge I am facing is how to relate the payment in Zoho Subscription back to the same user in Zoho Creator to update the paid account. 

I looked at using a webhook event of a new Zoho Subscription, The problem as I see it, how to make a reliable update back at Zoho Creator.  If the user used a different email when making a payment than the one they used to create the account back in creator I will have have two accounts in creator for the same person and a unrelated payment.

Is there a way to pass an identifier to the Subscription FORM and then have is passed back in the Webhook from Zoho Subscriptions