I haven’t been able to access any Delta flights using the flight offers search API. Is this something that is limited to production mode? Or am I searching wrong?

I’ve tried this request:

{
  "currencyCode": "USD",
  "originDestinations": [
    {
      "id": "1",
      "originLocationCode": "LAX",
      "destinationLocationCode": "JFK",
      "departureDateTimeRange": {
        "date": "2024-12-22",
        "start": "07:00:00",
        "end": "23:59:00"
      }
    }
  ],
  "travelers": [
    {
      "id": "1",
      "travelerType": "ADULT"
    }
  ],
  "sources": [
    "GDS"
  ],
  "searchCriteria": {
    "maxFlightOffers": 10,
    "flightFilters": {
      "cabinRestrictions": [
        {
          "cabin": "ECONOMY",
          "coverage": "MOST_SEGMENTS",
          "originDestinationIds": [
            "1"
          ]
        }
      ],
      "carrierRestrictions": {
        "includedCarrierCodes": [
            "DL"
        ]
      }
    }
  }
}

and have also tried searching for DL only in GET call.

to be returned:

{
    "meta": {
        "count": 0
    },
    "data": []
}