Additional Fees | create new fee ends in error 404

Joomla 6.1.3 | J2Commerce 6.6.1 | Additional Fee 6.0.6

After activation and try to create a first fee after clicking on save the following error appears:
404 not valid controller class: extrafee

Best regards
Jürgen

I tested the issue with PHP 8.3, 8.4 and 8.5, and the same error occurs with all three versions.

I also checked all released J2Commerce 6 versions of the Additional Fee plugin. The packages do not contain several assets that are referenced by the plugin code, including:

media/plg_j2commerce_app_extrafee/js/admin.js
media/plg_j2commerce_app_extrafee/js/variant-search.js
media/plg_j2commerce_app_extrafee/css/admin.css

In AppExtrafee.php there is also a comment explicitly stating that admin.js is intended to intercept task=extrafee.* requests and prevent Joomla's ComponentDispatcher from trying to call createController('Extrafee'), which would result in a 404.

This appears to correspond exactly to the error I am seeing when saving a new fee:

404 Invalid controller class: extrafee

As these files appear to be missing from all released J2Commerce 6 packages of Additional Fee, could you please check whether the required assets are missing from the release packages or whether there is another issue with the Joomla 6 controller routing?