ASP.NET MVC API接收请求但没有正确路由

I have an ASP.NET MVC API endpoint. When I test posting to it using content-type JSON, it works perfectly and the endpoint is hit. However, when I use content-type multipart/form-data, it does not work. I know the Request is being received by the server, because a breakpoint on Application_EndRequest in the global.asax is being hit. And I also know that wherever the request is being parsed by the server, it's doing it correctly, because my watch on the Request.Form object shows that the key-value pairs in the body ARE being deserialized properly. So why would the server be able to catch the incoming request and not correctly route it to my endpoint? I've been staring at this for a while, but despite the request being received and parsed by the server, the breakpoint on the endpoint's actual controller function is never hit.I have an ASP.NET MVC API endpoint. When I test