Python SDK: bulk user creation from CSV failing with 400 on phone numbers

We are scripting a bulk import of agents using the Genesys Cloud Platform SDK for Python. The script reads a CSV and iterates through rows to call user_api.post_users, but it returns a 400 Bad Request on the first run.

user = models.User(
 name=row['Name'],
 email=row['Email'],
 phone_numbers=[models.PhoneNumber(type="WORK", value=row['Phone'])]
)
client.user_api.post_users(body=user)

The error message states that the phone number format is invalid. The CSV contains E.164 formatted strings. Is the SDK expecting a different structure for the phone numbers array?