V2 Rest API Updating an address

Question about how to set state using the Rest V2 API

Here is an example of what I am posting for an address:

{“addresses”:[{“field”:“BILLING”,“line1”:“601 Alliance Ct”,“line2”:“”,“locality”:“Asheville”,“region”:“North Carolina”,“region_code”:“US-NC”,“zip_code”:“28806”}]}

If I pass a region code, I get a 400 error. When I omit the region_code, it completes with a 200, but the state is not shown in UI. This is the same region code I get when I request this contact record from Keap API.

I have tried passing both the region and region code, just the region and just the region code. When the region code is included I always get a 400. What am I missing?

The country_code and region_code fields use the ISO 3166-1 alpha-3 - Wikipedia and ISO 3166-2:US - Wikipedia ISO coding; I’m actually working in this area of our API at the moment and will add more descriptive documentation to the request object.

    "addresses": [
        "country": "United States of America",
        "country_code": "USA",
        "field": "BILLING",
        "line1": "123 E St",
        "postal_code": "85000",
        "region": "Arizona",
        "region_code": "US-AZ",
        "zip_code": "85000",
        "zip_four": "0000"