Cannot create or preview transaction using a customer with this email address

{
  "error": {
    "type": "request_error",
    "code": "subscription_customer_email_domain_not_allowed",
    "detail": "Cannot create or preview transaction using a customer with an unsupported email domain.",
    "documentation_url": "https://developer.paddle.com/errors/subscriptions/subscription_customer_email_domain_not_allowed"
  },
  "meta": {
    "request_id": "00000000-0000-0000-0000-000000000000"
  }
}