I need to get data from Sharepoint online list by using rest api.I will use the get and post method (post method in camel query case).

urlapp: the encoded url such as(https://name-29a8f2a9e3342d….)

$  .ajax({    url: urlapp+ "/../_api/web/lists/getbytitle('Letters')",     method: "GET",     headers: {         "accept": "application/json;odata=verbose",         "content-type": "application/json;odata=verbose",       },     async: false,     success: function (data) {         console.log(data);//Debug statement                      },     error: function (error) {         console.log(error);     } }); 

the previous code generate the 403 (Forbidden) error. After searching I found solution by using executeAsyn (new SP.RequestExecutor),but I need some way is sync execution not async.