I have discovered that in order to get this to work…Your Form fields themselves on webflow MUST have the same labels that you define your fields for an embedded form when building a list on Mail Chimp.
Here is a picture illustrating what I am talking about. My client built their Mail Chimp list form using these labels for each of their form fields. Frankly they labeled their form fields weird imo…and in all caps shudder
This is the only thing Webflow left out completely in their tutorial video. I just used logic to figure this out, and it makes sense… The Webflow forms field labels simply need to match up with whatever you create on Mail Chimp