Campaign ACS API "No match in backends for the given tenant id"

Hello!

I am working, for a customer, on a server side proxy in C# for the Campaign APIs and after fighting my way through the JWT authentication using the Microsoft jwt libraries I was ready to try out my first test following the examples here Campaign Standard: use APIs to optimize your cross-channel campaigns

I have built out the call as noted in the documentation... and so I am calling https://mc.adobe.io/<instance>.adobe.com/campaign/profileAndServices/service  where <instance> is my instance name.   I have previously created the integration in Adobe IO console.

When I make the call, though, all I get back is {"headers":{"X-Request-Id":"ngx.var.requestId"},"http_status":400,"message":"No match in backends for the given tenant id."}

What am I missing?

Thanks,

Thom

Below is the code that makes the call

public async Task<SubscriptionServiceList> GetAvailableSubsriptionServicesAsync() {

            SubscriptionServiceList result = new SubscriptionServiceList();

            ApiAccessToken AccessToken = GetAccessToken();

            result.AsOfDate = DateTime.Now;

            HttpClient client = new HttpClient();

            var httpRequestMessage = new HttpRequestMessage {

                Method = HttpMethod.Get,

                RequestUri = new Uri(ServiceListingEndpoint),

                Headers = {

                    {HttpRequestHeader.ContentType.ToString(),"application/json" },

                    { HttpRequestHeader.Authorization.ToString(), AccessToken.HttpRequestHeaderText },

                    { HttpRequestHeader.CacheControl.ToString(), "no-cache" },

                    { "X-Api-Key", APIKey }

                }

            };

            Task<HttpResponseMessage> t = client.SendAsync(httpRequestMessage);

            t.Wait();

            HttpResponseMessage response = t.Result;

            using (HttpContent respContent = response.Content) {

                string toLoad = await respContent.ReadAsStringAsync();

                System.Diagnostics.Debug.WriteLine (toLoad)

                //TODO load string into JSON object for parsing and load response value

            }

            return result;

        }