Example for a free sub.

 {
    "promotionSource": "FREEINDEF",
    "publication": "00002800",
    "quantity": 1,
    "customerPurchaseOrderNumber": "52",
    "customerPurchaseOrderType": "I",
    "customerPurchaseOrderDate": "2021-01-19",
    "validFrom": "2021-02-24",
    "paymentMethod": "R",
    "inputOffice": "IMM-INPUT",
    "inputDate": "2021-01-15",
    "inputUser": "SYS-RFC",
    "externalOrderNumber": "52",
    "saveInSystem": true,
    "postAtOnce": true,
    "subscriptionRenewal": {
        "automaticRenewal": false
    },
    "bpRelations": [
        {
            "role": "AG",
            "bp": {
                "lastName1": "Vogt",
                "firstName": "Anja",
                "salutationCode": "02",
                "addressLine1": "Konrad-Zuse-Straße 3",
                "addressLine2": "",
                "addressLine3": "",
                "city": "Neckarsulm",
                "regionText": "",
                "regionCode": "",
                "zipcode": "74172",
                "countryCode": "DE",
                "bpCommunicationsList": [
                    {
                        "communicationType": "WW",
                        "communicationValue": "vogt@dsb-ccb.net"
                    }
                ]
            }
        }
    ]
}