One-off discount not valid for subscription

{
  "error": {
    "type": "request_error",
    "code": "subscription_one_off_discount_not_valid",
    "detail": "one-off discount invalid for subscription",
    "documentation_url": "https://developer.paddle.com/errors/subscriptions/subscription_one_off_discount_not_valid"
  },
  "meta": {
    "request_id": "00000000-0000-0000-0000-000000000000"
  }
}