In the old sqPaymentForm I could populate the zip code. I have not found any way to do that with the web payments SDK. Am I missing something?
With the Web Payments SDK you can set a zip code value in the CardOptions. 
Amazing!! Thank you for your help! I have another question, but I’ll post as a different topic.
How to display the postal code input?
Ah never mind! I found the explanation in the doc here: Migrate to the Web Payments SDK
* **Dynamic postal code field.** You do not need to determine whether your application must provide and validate the buyer postal code. The SDK shows this field based on the buyer's card number. Your application code does not make this determination.