Adding multiple form fields to Mailchimp with Logic

I connected my newsletter sign up form to my Mailchimp account following this tutorial in webflow university. It only has an email tag in the body area of the HTTP request. I can’t get it to add first and last name. I have tried using FNAME and first_name as the possible descriptors (or whatever you call them, sorry, I don’t know official coding words) and neither is working. The former is how it is labled in mailchimp and the latter is the form field labels in my webflow form. It does import the email address with no issues when I test the logic flow, but it wont do any other fields.

How do I connect all the data from the webflow form to the new mailchimp subscriber?