var appURL = '';
   appURL = serverURL + $backendApis[apiName] + "/?_s=" + $http.defaults.headers.common['Session-Alias'];

         return $http.post(appURL, postParams).success(function(response, status, headers, config) {

            $http.defaults.headers.common['Custom-Access-Token'] = headers('Custom-Access-Token');
            if (response.errorCode && response.errorCode != "8233" && response.errorCode != "506717") {
                alert("Sorry, we are not able to provide you a quotation at this stage as we are facing a technical issue. Please get back after sometime to issue a quotation or call us. Sorry for the inconvenience");
            }
        });

var promises = urls(); //all your urls in an array

function doCall(){

   var appUrl = promises.pop();
   $http.post(appURL, postParams).success(function(response, status, headers, config) {

        $http.defaults.headers.common['Custom-Access-Token'] = headers('Custom-Access-Token');
        if (response.errorCode && response.errorCode != "8233" && response.errorCode != "506717") {
            alert("Sorry, we are not able to provide you a quotation at this stage as we are facing a technical issue. Please get back after sometime to issue a quotation or call us. Sorry for the inconvenience");
        }
    }).then(function(){
        if(!promises.length) //no urls left, kill the process.
          return;

        doCalls(); //go ahead for the next one
    });
}