Introductory Offer "Countries or Regions" setup issue

I'm experiencing issue during Introductory offer creation. Steps to reproduce:

1. Press 'Set up Introductory Offer'
2. Select all Countries or Regions for Introductory Offer
3. Select Start Date and End Date
4. Select type of Introductory Offer: Free, Duration: 1 week
5. Confirm

Result: Several rows have blank Countries or Regions fields.

"An error has occurred. Try again later." is shown.

Response is 409 status code, response is array of

[
  {
    "id": "77cdf09d-21f8-4acb-89e9-2123f40925da",
    "status": "409",
    "code": "ENTITY_ERROR.RELATIONSHIP.REQUIRED",
    "title": "The provided entity is missing a required relationship",
    "detail": "You must provide a value for the relationship 'territory' with this request",
    "source": {
      "pointer": "/data/relationships/territory"
    }
  },
  ...
]