Python SDK user.create throws 400 when looping through CSV users

Trying to bulk-create agents from a CSV dump using the Python SDK. The logic seems straightforward, but the API keeps rejecting the payload with a 400 error on the second iteration. First user creates fine, subsequent ones fail. I’m reusing the same user_api client instance. Here’s the snippet causing the headache:

import csv
from genesyscloud import user_api

api = user_api.UserApi(api_client)
with open('agents.csv') as f:
 reader = csv.DictReader(f)
 for row in reader:
 body = api.create_user_request(
 first_name=row['first'],
 last_name=row['last'],
 email=row['email'],
 user_type='agent'
 )
 api.post_users(body=body)

The error log just says Invalid user email address even though the emails in the CSV are valid and unique. I’ve checked the formatting, no extra spaces. Is the SDK caching something or is there a rate limit I’m hitting without a 429? The first row goes through without issue. Subsequent rows fail immediately. No helpful stack trace. Just a generic validation error.