Uploading a file for a Request

Currently coding in C# and I am having trouble figuring out how to attach a token returned from Uploads API to a new Request. I have two service methods that have been tested on Postman and work as expected on their own; RequestTicket and UploadAttachment. RequestTicket allows an end user to make a ticket request by calling the /api/v2/requests endpoint using Request API and UploadAttachment calls the /api/v2/uploads endpoint to get the upload token. 

public async Task<string> RequestTicket(string comment)
        {
            // Construct the ticket payload and the request URI
            var zendeskTicket = new TicketSSO(comment, _userResolver.CurrentStaff);

            var requestUri = $"{_zendeskClientConfig.Url}/requests";

            // Create the request message for POSTing the ticket to Zendesk
            _zendeskHttpRequest.CreateRequestMessage(HttpMethod.Post, requestUri, zendeskTicket.BuildJsonRequest());

            // Send the request
            var response = await _zendeskHttpClient.SendAsync(_zendeskHttpRequest);
            return response;
        }

public async Task<string> UploadAttachment(string filePath, string fileName)
        {
            // Create the file payload
            var file = new UploadSSO(filePath);

            // Construct the request URI for uploading an attachment
            var requestUri = $"{_zendeskClientConfig.Url}/uploads.json?filename={fileName}";

            // Create the request message for POSTing a new file upload
            _zendeskHttpRequest.CreateRequestMessage(HttpMethod.Post, requestUri, file.BuildJsonRequest());

            // Send the request and upload an attachment
            var response = await _zendeskHttpClient.SendAsync(_zendeskHttpRequest);

            Console.WriteLine("Response: ", response);

            return response;
        }