Create mandate with mandatereference

var bankAccountIban = new BankAccountIban();
bankAccountIban.Iban = "DE46720200700359736690";

var contactDetails = new MandateContactDetails();
contactDetails.EmailAddress = "wile.e.coyote@acmelabs.com";

var mandateAddress = new MandateAddress();
mandateAddress.City = "Monumentenvallei";
mandateAddress.CountryCode = "NL";
mandateAddress.Street = "Woestijnweg";
mandateAddress.Zip = "1337XD";

var name = new MandatePersonalName();
name.FirstName = "Wile";
name.Surname = "Coyote";

var personalInformation = new MandatePersonalInformation();
personalInformation.Name = name;
personalInformation.Title = "Miss";

var customer = new MandateCustomer();
customer.BankAccountIban = bankAccountIban;
customer.CompanyName = "Acme labs";
customer.ContactDetails = contactDetails;
customer.MandateAddress = mandateAddress;
customer.PersonalInformation = personalInformation;

var body = new CreateMandateRequest();
body.Customer = customer;
body.CustomerReference = "idonthaveareference";
body.Language = "nl";
body.RecurrenceType = "UNIQUE";
body.SignatureType = "UNSIGNED";

var response = await client.V1.WithNewMerchant("merchantId").Mandates.CreateWithMandateReference("42268d8067df43e18a50a2ebf4bdb729", body);

{
    "mandate" : {
        "customerReference" : "idonthaveareference",
        "customer" : {
            "bankAccountIban" : {
                "iban" : "DE46720200700359736690"
            },
            "mandateAddress" : {
                "street" : "Woestijnweg",
                "city" : "Monumentenvallei",
                "zip" : "1337XD",
                "countryCode" : "NL"
            },
            "companyName" : "Acme labs",
            "contactDetails" : {
                "emailAddress" : "wile.e.coyote@acmelabs.com"
            },
            "personalInformation" : {
                "name" : {
                    "firstName" : "Wile",
                    "surname" : "Coyote"
                },
                "title" : "Miss"
            }
        },
        "recurrenceType" : "UNIQUE",
        "status" : "ACTIVE",
        "uniqueMandateReference" : "42268d8067df43e18a50a2ebf4bdb729"
    }
}

{
    "errorId" : "15eabcd5-30b3-479b-ae03-67bb351c07e6-00000092",
    "errors" : [
        {
            "code" : "20000000",
            "propertyName" : "customer.billingAddress.street",
            "message" : "PARAMETER_NOT_FOUND_IN_REQUEST"
        }
    ]
}

{
    "errorId" : "98281bc6-5cb2-4ffe-b835-6a3425b06dff-00000df2",
    "errors" : [
        {
            "id" : "MANDATE_ALREADY_EXISTS",
            "code" : "8888888",
            "category" : "MANDATE_PLATFORM_ERROR",
            "propertyName" : "uniqueMandateReference",
            "message" : "A mandate with that reference already exists",
            "httpStatusCode" : 409
        }
    ]
}