Automation to send an email produces "'to' field is empty"

Hello! I’m trying to make an automation where an email is sent to a linked record whenever a specific field in a record changes. My trigger tests fine, but I can’t set up an action because whenever I try to test it tells me the “to field is empty.” I have a lookup field to pull the emails for the linked records, and because I read that lookup fields don’t work with automations, I created a formula field that’s pulling in the emails and that’s what I’m trying to reference with my action, but for whatever reason it won’t recognize the email in the field.

It’s probably still an array. Use something like arrayjoin to make sure the field is a string.