How to add Authorization header to external REST API call from server script

It,s easy, try that

function doGet() {
myFunction();
}
function myFunction() {
var url = “https://onesignal.com/api/v1/notifications”;

var D = {
app_id:“OneSignalAppID”,
// include_player_ids : [“1bd1227a-ff50-478c-b097-b2a673c8c817”],
included_segments:[“All”],
headings:{“en” : “FaucetSatoshi”},
contents: {“en” : “PLAYER”},
data: {“type”: “phoneNumber”}
};
var payload = JSON.stringify(D);

var headers = { “Accept”:“application/json”,
“Content-Type”:“application/json”,
“Authorization”:“Basic RESTAPIKey”,

         };

var options = { “method”:“POST”,
“headers”: headers,
“payload” : payload
};
var response = UrlFetchApp.fetch(url, options);
Logger.log(response);

}