Please follow the steps below

  1. Go to the general configuration page
  2. Select an option where the add-in will get users list. There are 3 options type
    1. If all users in site. Select All user in site
    2. If all users in users info list. Select Users from List 'Manage Users information'
    3. If all users in SharePoint Group. Select another

If you select the SharePoint Group, Please make sure that "Who can view the membership of the group?" in Group Settings is everyone