此CORS设置有什么问题？

Question

我有以下API可以验证mySQL表中的电子邮件地址。

。 。

 [EnableCors(origins: "http://www.demo.MainSite.com, always", headers: "*", methods: "*", SupportsCredentials =true)]
    public class StarSystemController : ApiController
    {
        DataConnection oDataConnection { get; set; }


        [AllowAnonymous]
        [HttpPost]
        [Route("api/Starsystem/UserExists")]
        public string IsUserNameExists(W_Email Email)
        {
            CreateDataConnection();
            bool result = oDataConnection.IsUserNameExists(Email);
            string output = JsonConvert.SerializeObject(result);
            return output;
        }

API在Postman和Swagger中工作正常。但是，当我在Angular代码中调用此代码时，会出现以下错误。

Failed to load resource: net::ERR_CONNECTION_RESET

main.53cb435a591be8fbffcf.js：1错误

t {headers: n, status: 0, statusText: "Unknown Error", url: null, ok: false, …}
    error: ProgressEvent {isTrusted: true, lengthComputable: false, loaded: 0, total: 0, type: "error", …}
    headers: n {normalizedNames: Map(0), lazyUpdate: null, headers: Map(0)}
    message: "Http failure response for (unknown url): 0 Unknown Error"

    name: "HttpErrorResponse"
    ok: false
    status: 0
    statusText: "Unknown Error"
    url: null
    __proto__:
    constructor: ƒ t(t)
    __proto__: Object

我无法弄清楚它的确切来源。任何帮助表示赞赏。

我在ASP.net后端中遵循以下站点进行CORS设置。 MVC web api: No 'Access-Control-Allow-Origin' header is present on the requested resource