retrieve Facebook app request ID from FB.GetAppLink result callback

Hello ,
i’m wondering what is the best way to retrieve an app request ID from an Iapp link result , i use unity facebook sdk , and when i use the code provided in facebook documentation section , this one i mean
https://developers.facebook.com/…/ref…/current/FB.GetAppLink

FB.GetAppLink(DeepLinkCallback);

void DeepLinkCallback(IAppLinkResult result) {
if(!String.IsNullOrEmpty(result.Url)) {
var index = (new Uri(result.Url)).Query.IndexOf("request_ids");
Debug.Log("index "+index );
if(index != -1) {
//
}
}
}

i get index =-1
i have attached an image of what result.RawResult looks like ,
please i need some help

up !!