Compatibilty plugin and hikaserial

-- url of the page with the problem -- : www.volvokv.nl
-- HikaShop version -- : 5.6.1
-- HikaSerial version -- : 5.0.0
-- Joomla version -- : 5.3.0
-- PHP version -- : 8.3.14
-- Browser(s) name and version -- : Firefox
-- Error-message(debug-mod must be tuned on) -- : Class "JPlugin" not found.

When testing for not using the compatibility plugin I think there is an error for the plugin Serial Private Content - HikaSerial ; This plugin extends JPlugin an not hikaserialPlugin. After installing hikaserial in a test environment I cannot go to the plugins;

regards