我试图在C#中请求一个oAuth令牌，做的正是Postman（它工作的地方）正在做的事情，但我一直得到未经授权。我不知道Postman做的有什么不同。

下面是我的代码：

var request = new HttpRequestMessage(HttpMethod.Post, "https://myapi/OAuth/Token/")
        {
            Content = new FormUrlEncodedContent(new KeyValuePair<string?, string?>[]
            {
                // new("client_id", _clientId),
                // new("client_secret", _clientSecret),
                // new("scope", "company-api"),
                new ("Content-Type", "application/x-www-form-urlencoded"),
                new("grant_type", "client_credentials")
            })
        };

        _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", System.Convert.ToBase64String(Encoding.ASCII.GetBytes($"{_clientId}:{_clientSecret}")));

        using var response = await _httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
        response.EnsureSuccessStatusCode();
        await using var responseContentStream = await response.Content.ReadAsStreamAsync();

        var accessToken = await JsonSerializer.DeserializeAsync<AccessToken>(
            responseContentStream, JsonSerializerOptions.Default);

以下是我在postman中的设置：