sending.cs

public async Task<DataResponse> GetAsync(string uri, List<KeyValuePair<string, string>> formValues) {
            try {
                var auth = new AuthenticationHeaderValue("Basic",
                    Convert.ToBase64String(Encoding.UTF8.GetBytes(
                        $"{HttpUtility.UrlEncode(_clientId)}:{HttpUtility.UrlEncode(_clientSecret)}")));
                var request = new HttpRequestMessage(HttpMethod.Post, uri) {
                    Headers = { Authorization = auth },
                    Content = new FormUrlEncodedContent(formValues)
                };
                using var response = await HttpClient.SendAsync(request);
                var content = await response?.Content?.ReadAsStringAsync() ?? "";
                if(!response.IsSuccessStatusCode) {
                    LogWarn($"Request: {request} {await request.Content.ReadAsStringAsync()}");
                    LogWarn($"Response: {response} - {response.StatusCode} - {response.ReasonPhrase}: {content}");
                }
                response.EnsureSuccessStatusCode();
                if(string.IsNullOrEmpty(content)) {
                    throw new ArgumentNullException(nameof(content));
                }
                return JsonSerializer.Deserialize<DataResponse>(content);
            }
            catch(Exception ex) {
                var errorValueBuilder = new StringBuilder();
                foreach(var kv in formValues) {
                    errorValueBuilder.AppendLine($"{kv.Key}:{kv.Value}");
                }
                LogWarn(errorValueBuilder.ToString());
                LogError(ex);
                throw;
            }

        }