如何修复Unity WebRequest未知错误

Question

I have problem with the code below when I do request to my laravel api in unity.

I added this headers to location ~ .php$ in conf

add_header 'Access-Control-Allow-Origin' "*";
add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT,OPTION';
add_header 'Access-Control-Allow-Credentials' "true";
add_header 'Access-Control-Allow-Headers' "x-authorization, Content-Type, Accept, X-Access-Token, X-Application-Name, X-Request-Sent-Time";

I have also set response headers in filter php app::After function. php laravel

    $response->headers->set('Access-Control-Allow-Headers','x-authorization, Content-Type');
    $response->headers->set('Access-Control-Allow-Methods','GET, POST, PUT, OPTIONS');
    $response->headers->set('Access-Control-Allow-Origin','*');

c#

    WWWForm form = new WWWForm();
    form.AddField("email", email_id);
    form.AddField("password", password);
    www2.certificateHandler = new 
    AcceptAllCertificatesSignedWithASpecificKeyPublicKey();
    www2.chunkedTransfer = true;
    yield return www2.SendWebRequest();
    Debug.Log("downloadHandler Text : " + www2.downloadHandler.text);
    Debug.Log("responseCode : " + www2.responseCode);
    Debug.Log("isDone : " + www2.isDone);
    Debug.Log("method : " + www2.method);

Debug is downloadHandler Text : responseCode : 0 isDone : True method : POST error: Unknown error

I think there would be a settings needs to change in the ubuntu server. From my understanding it is ssl issue that unity wants to know the servers certificate. Could you please help? Thanks a lot.