Custom Fields in the Cart or Checkout of Dawn theme

Retired Boards Appdev Store Design
1

I’m trying to add a “How did you hear about us?” field in the cart. Pretty sure I can’t do it at checkout unless I have Plus. I tried adding a HTML select menu to the main.cart.items.liquid section, but it just throws an error.

This is the code I’m using right after the closing table element:
2

I am having the same issue with the same theme. I used third party app SmartCA: Customer Attribute.

Hope that helps.