the remote server error (401) Unauthorized while uploading a file using c# -

i trying upload file server giving me 401 error , here code.

static void main(string[] args) {     string key = "ewh6r-u61eveh4kjrx4qizvjanru4qgz";     string input = @"e:\new folder\untitled_1.png";     string output = @"e:\new folder (2)\untitled_1.png";      string url = "https://api.tinify.com/shrink";     webclient client = new webclient();     //  httpwebrequest client = (httpwebrequest)webrequest.create(url);     //  client.keepalive = false;     // client.contenttype = "application/x-www-form-urlencoded";     // client.method = "post";     //  client.timeout = system.threading.timeout.infinite;     //  client.credentials = new networkcredential("?", "?");     client.usedefaultcredentials = false;     string auth = convert.tobase64string(encoding.utf8.getbytes("api:" + key));     client.headers.add(httprequestheader.authorization, "basic" + auth);     //string input1 = @"key=gtthtxceq7shvgfl-afy_w_trnhhgml3&image=" + convert.tobase64string(file.readallbytes(input));     // string input3 = input1+auth;     // byte[] bytes = encoding.utf8.getbytes(input1);     // stream os = null;     try     {         // client.contentlength = bytes.length;         //  os = client.getrequeststream();         //  os.write(bytes, 0, bytes.length);         client.uploaddata(url, file.readallbytes(input));         // client.uploadfile(url, "post", input);         client.downloadfile(client.responseheaders["location"], output);     }     catch (exception e)     {         console.writeline("compression failed " + e.message);     }  }` 

you missed space character between word "basic" , authorization key when building authorization header string:

client.headers.add(httprequestheader.authorization, "basic " + auth);