Platform SDK for Python bulk user creation from CSV throwing 400

Trying to bulk-create users from a CSV using the Genesys Cloud Platform SDK for Python. The script loops through rows and calls users_api.create_user(user_obj). It works for the first few, then fails with 400 Bad Request and error_code: "validationFailed". The user_obj looks identical to the working ones. Is there a rate limit or a hidden validation rule in the SDK wrapper? Here’s the snippet:

user = models.User()
user.email = row['email']
users_api.create_user(user)

Stuck on this.