I am new to Zapier and trying to set up a trigger from A) Stripe customer payments for digital product to 
A Convertkit sequence for purchasers of this digital product.
It was going well and seemed to all be connected but none of my purchasers in Stripe are getting zapped over to the convertkit sequence.
I think it has to do with the ACTION STEP, specifically, EMAIL, FIRST NAME + NULL .
What goes in these fields?? I can't find it anywhere. I do not understand what email goes here and why.