How to combine url and string for api call [duplicate]

I'm trying to combine a url and string at runtime and then call it.

public static Uri Append(this Uri uri, params string[] paths)
    {
        return new Uri(paths.Aggregate(uri.AbsoluteUri, (current, path) => string.Format("{0}/{1}", current.TrimEnd('/'), path.TrimStart('/'))));
    }

var url = new Uri("https://127.0.0.1:2999/liveclientdata/playerscores?summonerName=").Append(_PlayerName).AbsoluteUri;

However when I call it, this error is returned:

Failed the request: HTTP/1.1 400 Bad Request

The url looks like this

https://127.0.0.1:2999/liveclientdata/playerscores?summonerName=/%22KidKiwi91%22

I know the error is caused by the concatenation of the url and string because it I make it all one url and not combine them in runtime it works.

Other things i've tried:

string url = "urlgoeshere=" + playername;
string url = UnityWebRequest.EscapeURL("urlgoeshere" + playername);

string url_q = "urlgoeshere=" + playername;
var url=new Uri(url_q);

It's called using this

private IEnumerator GetJSON(string url, System.Action<string> callback)
    {
        failed = false;

        //Debug.Log(url);
        using (UnityWebRequest webRequest = UnityWebRequest.Get(url))
        {
            webRequest.certificateHandler = new BypassCertificate();

            yield return webRequest.SendWebRequest();

            string error = webRequest.error;

            if (error != null)
            {
                Debug.Log("Failed the request: " + error);
                failed = true;
            }
            else
            {
                callback?.Invoke(webRequest.downloadHandler.text);
                //Debug.Log(webRequest.downloadHandler.text);
            }
        }
    }

Any ideas?

Thanks