SOAP service - Cannot convert source type [Something[]] to target type [Something]

I am consuming a 3rd party SOAP service into my C# .NET Core console application.

To do so, I added in the service reference, by importing the WSDL (Add --> Connected Service --> WCF Web Service).

The service exposes a method called "Order", which takes in an OrderRequest parameter

OrderResponse Order(OrderRequest request);

And the OrderRequest is defined like this:

public partial class OrderRequest
{    
    private string fMethod;    
    private KVPfield[] searchFields;
}

Nothing too exciting about the KVPfield object, it just looks like this:

public partial class KVPfield 
{
    private string fKey;
    private string fValue;
}

So in my mind, EASY, just define an array of KVPfield's and assign that to the OrderRequest:

var orderReq = new OrderRequest();
orderReq.fMethod = "save";

orderReq.searchFields= new KVPfield[] {
    new KVPfield() { fKey = "EPID", fValue = "XY111359" },
    new KVPfield() { fKey = "VSN", fValue = "HTP000157A" }
};

But now when I execute the method

var resp = svc.Order(orderReq);

But then it throws the following error:

System.ServiceModel.CommunicationException: 'There was an error in serializing body of message OrderRequest: 'CodeGenError(IsNotAssignableFrom): Cannot convert source type [svc.KVPfield[]] to target type [svc.KVPfield].'.

Why if my WSDL's is asking for an ARRAY of KVPfield, is it expecting a single KVPfield?

Is it something to do with how I am defining my KVPfield[], or something in the internals of the wsdl?