ASP.NET oData patchValue received from Angular is

I'm developing an app with an Angular based front-end and an ASP.NET back end using oData and Oracle. I'm at the point where I'm trying to patch records on the back end. I'm using generic boilerplate code on the back end in my controller and the patch method looks like this:

  <AcceptVerbs("PATCH", "MERGE")>
    Async Function Patch(<FromODataUri> ByVal key As Decimal, ByVal patchValue As Delta(Of FTP_ORDERS)) As Task(Of IHttpActionResult)
        Validate(patchValue.GetEntity())

        If Not ModelState.IsValid Then
            Return BadRequest(ModelState)
        End If

        Dim fTP_ORDERS As FTP_ORDERS = Await db.FTP_ORDERS.FindAsync(key)
        If IsNothing(fTP_ORDERS) Then
            Return NotFound()
        End If

        patchValue.Patch(fTP_ORDERS)

        Try
            Await db.SaveChangesAsync()
        Catch ex As DbUpdateConcurrencyException
            If Not (FTP_ORDERSExists(key)) Then
                Return NotFound()
            Else
                Throw
            End If
        End Try

        Return Updated(fTP_ORDERS)
    End Function

On the Angular side, I'm using $resource based service to send the update. The code that calls the resource looks like this:

 (new FTPOrderService({
                    "key": vm.ID,
                    "data": vm
                }, vm))
                    .$patch()
                    .then(function (data) {
                        alert("Order Saved!");
                    },
                        function (error) {
                            debugger;
                        }
                        );

The service is defined with:

.factory('FTPOrderService', function ($resource) {
        var odataUrl = '../odata/FTP_ORDERS';
        var results = $resource('', {}, {
            'patch': {
                method: 'PATCH',
                params: {
                    key: '@key',
                },
                url: odataUrl + '(:key)'
            }
        });

        return results;
    })

I've also tried:

(new FTPOrderService({
                    "key": vm.ID,
                }, vm))
                    .$patch(vm)
                    .then(function (data) {
                        alert("Order Saved!");
                    },
                        function (error) {
                            debugger;
                        }
                        );

and get the same results.

I believe that I have configured angular to send the data properly with:

.config(['$httpProvider', function ($httpProvider) {
        $httpProvider.defaults.headers.patch = {
            'Content-Type': 'application/json;charset=utf-8'
        };
    }])

The debugger shows that I'm calling the URL with the appropriate key appended to it in parens and the request payload looks like this:

{key: "1239990990", data: {loading: false, selectedRow: {}, lineItems: [,…], orderId: "1239990990",…}}
data: {loading: false, selectedRow: {}, lineItems: [,…], orderId: "1239990990",…}
key: "1239990990"

Any idea of what I'm missing? There are numerous examples out there using direct calls to $http.post and a few for .patch, but nothing current using $resource.

I am not entirely sure what the cause of this issue was, but in tracing it, I did discover that intermittently an object was not being received by the patch method in .NET. The object I'm passing in is particularly heavy and what I was passing by default was actually heavier than what the ASP.NET side of the app requires. Adding code prior to the patch call to assemble an object that meets the requirements at a minimum level resolved the issue.