response error = System.Net.Http.HttpRequestException: Request failed with status code Unauthorized
response content = {"type":"invalid_client","title":"The client_id is invalid or authentication failed.","status":401,"instance":"/token","operationId":"0693561ea73341aa9cebd7a6ac2082c3","traceId":"00-e07b4fca33480b4689f70fa1db377455-d9acabc8fc3a3e4b-00"}
Line 234 successful

apitoken for swagger  = {"type":"invalid_client","title":"The client_id is invalid or authentication failed.","status":401,"instance":"/token","operationId":"0693561ea73341aa9cebd7a6ac2082c3","traceId":"00-e07b4fca33480b4689f70fa1db377455-d9acabc8fc3a3e4b-00"}
 

Here is the error. I checked both of those things you mentioned and they are correct. I am in Canada so my domain changes to .ca and the function GetSigningCredentials requires only the JWK portion of the JSON object to be sent. 

Here is some code to reference from the project. I am using the library RestSharp. 

string key = File.ReadAllText(@"LF API CloudAccessKey.json");//ServiceKey downloaded from App Configuration Authentication, placed on same folder as this app
            string token = CreateClientCredentialsAuthorizationJwt(clientId, servicePrincipalKey, new JsonWebKey(key));
            Console.WriteLine(token + "\n");

            var client = new RestClient($"https://signin.laserfiche.ca/oauth/token");
            

            var request = new RestRequest();
            request.Method = Method.Post;

            request.AddHeader("Authorization", $"Bearer {token}");
            request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
            request.AddHeader("grant_type", "client_credentials");
            request.AddParameter("application/x-www-form-urlencoded", "grant_type=client_credentials", ParameterType.RequestBody);
            request.RequestFormat = DataFormat.Json;

            try
            {
                RestResponse response = client.Execute(request);

                Console.WriteLine("response error = " + response.ErrorException);
                Console.WriteLine("response content = " + response.Content);

                string apiToken = (response.Content);
                
                Console.WriteLine("apitoken for swagger  = " + apiToken);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

Hi Jason, I have duplicated the same result as Brandon.

Here is what I did:

1. A new demo account;

2. A Service user account for testing;

3. Registered a new Service App and then create the Service key

4. Following all the step from https://developer.laserfiche.com/guide_service-principals.html  to generate a JWT use the C# code sample (JWT verified via https://jwt.io/ that decoded as exact same before encoding)

5. Use both Brandon's code and use plain "WebClient" to do a post at "https://signin.laserfiche.ca/oauth/token"  get exactly same error  "401" error

6. Use postman with JWT generated by code sample get the same "401" error

So basically it's not working on our end -- could it be account related? let us know.