你必须看看 C# 调用返回给你什么对吗?

You have to look what C# call returns to you right ?

我不懂 C#，但我不认为 json 必须在 $_POST 变量中发送，而是在请求的正文部分中发送.在香草 PHP 中，您可以通过以下方式获得它:

I don't know C# but I don't think the json must be send in the $_POST variable but in the body part of the request. In vanilla PHP you can get it with :

file_get_contents('php://input');