Python SDK bulk user creation failing with 400

Running a loop to bulk create users via the Python SDK. The post_users call returns a 400 Bad Request. The error payload points to address.line1 being missing, but the CSV has it populated. Here’s the snippet:

from genesyscloud.users import UsersApi

users_api = UsersApi(configuration)
for row in csv_data:
 user = User(
 name=row['name'],
 email=row['email'],
 address=Address(line1=row['line1'])
 )
 users_api.post_users(body=user)

The API docs say line1 is optional, so why is it failing?