Magento – Magento 2 : How to add address attribute in checkout new address form

It might be worth adding your code fully to inspect. However, I dont think your Layout Handle is correct for the action you are trying to access.

customer_address_editstaff might be what you need to associate to a controller providing your URL structure.

I've been looking for the same info and I found that Magento has something similar in their documentation:

http://devdocs.magento.com/guides/v2.0/howdoi/checkout/checkout_new_field.html

Maybe this could help you or help someone else.

Greetings.