AngularJS: checkbox ngModel not checking

Question

There seems to be a problem with the ngModel.

I'm trying to get the selected checkbox IDs but it's not saving because their checked property isn't changed by the ngModel.

These are only partial code snippets. When I turned one of the checked values into true, the ID saved into the checkbox array (addCustom function runs when a button is clicked).

How do I fix this so that I could get the selected checkboxes?

$scope.checkboxData = [{
  name: "Computer Crash",
  id: 1,
  checked: false
}, {
  name: "Computer Restart",
  id: 2,
  checked: false
}];


$scope.addCustom = function() {
  $scope.custom = !$scope.custom; // close modal

  // get checkbox id
  $scope.checkboxArray = [];

  $scope.checkboxData.forEach(function(checkbox) {
    if (checkbox.checked) {
      console.log(checkbox.id);
      $scope.checkboxArray.push(checkbox.id);
    }
  })
  console.log($scope.checkboxArray);

  //////

  $scope.data.push({
    name: $scope.name,
    symptom: $scope.checkboxArray,
    answer: $scope.answer
  });
  localStorage.setItem('data', JSON.stringify($scope.data));
};

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.20/angular.min.js"></script>
<div ng-app="Netsafe" ng-controller="activityController">
  <div ng-repeat="checkbox in checkboxData" class="form-check form-check-inline col-sm-4">
    <label>
      <input type="checkbox" ng-model="checkbox.checked"/>
      {{checkbox.name}}
    </label>
  </div>
</div>