Exception: Class Not Found in PHP

I get the error:

Exception – Class ‘sitesoutputtab_gamify’ not found when load an edit page.

I have a file named sites/classes/output/edit.php with something like:

<?php

namespace sitesoutput;

class edit extends tabs {

      public function __construct(array $attributes = []) {
             parent::__construct($attributes);

             ...
             ...
             $this->add_tab(new tab_gamify($attributes));
      }

}

And a file named sites/classes/output/tab_gamify.php with something like:

<?php

namespace sitesoutput;

class tab_gamify extends tab {
      ...
      ...
}

I get the previous error message and and i not able to locate my error. Any suggestion or clue will be very appreciated.

Thanks in advance for your time.

I’ve revised namespaces, also reloaded and restarted docker container.