Warning: require(vendor/autoload.php): Failed to open stream: No such file or directory in /var/app/current/classes/s3.php on line 5

Fatal error: Uncaught Error: Failed opening required 'vendor/autoload.php' (include_path='.:/usr/share/pear:/usr/share/php') in /var/app/current/classes/s3.php:5
Stack trace:
#0 /var/app/current/classes/group.php(3): require_once()
#1 /var/app/current/appheader.php(35): require_once('...')
#2 /var/app/current/search.grid.3.php(2): require_once('...')
#3 {main}
  thrown in /var/app/current/classes/s3.php on line 5