The remote server returned an error 429

Hello. Yesterday is working fine, but now there show me this error The remote server returned an error 429.

How can fix the error.

string urltocken = "https://www.wix.com/oauth/access";

var shopAccessToken = UserInt.Value;

using (var streamWriter = new StreamWriter(myReqtoken.GetRequestStream()))

{

string json = new JavaScriptSerializer().Serialize(new

{

grant_type = "refresh_token",

client_id = UserInt.ApiKey,

client_secret = shopAccessToken,

refresh_token = UserInt.Token

});

streamWriter.Write(json);

}

Here is the error -------> WebResponse wrtoken = myReqtoken.GetResponse();