Illegal characters in path.

I want to consume a service at http://www.esvapi.org/api/#sample. The sample code in the link is

C#
REST

StringBuilder sUrl = new StringBuilder();
sUrl.Append("http://www.esvapi.org/v2/rest/passageQuery");
sUrl.Append("?key=IP");
sUrl.Append("&passage=" + Server.UrlEncode("Matthew 5").ToString());

sUrl.Append("&include-headings=true");

WebRequest oReq = WebRequest.Create(sUrl.ToString());
StreamReader sStream = new StreamReader(oReq.GetResponse().GetResponseStream());

StringBuilder sOut = new StringBuilder();
sOut.Append(sStream.ReadToEnd());
sStream.Close();

Response.Write(sOut.ToString());

I rewrote it with my own.

var strSearch = "John 3:16";
    var options = "include-passage-references=true";
    var client = new WebClient();
    var query = string.Format("www.esvapi.org/v2/rest/passageQuery?key={0}&passage={1}&options={2}", "IP", Server.UrlEncode(strSearch), options);
    var result = client.DownloadString(query);

However I got an exception which is "System.ArgumentException: Illegal characters in path."

The variable query is

www.esvapi.org/v2/rest/passageQuery?key=IP&passage=John+3%3a16&options=include-passage-references=true

What is wrong?