I have followed the implementation guide in SAP Help ( link below) and checked my implementation multiple times.
So I have also checked, that the name of the event handler in method lo_api_controller->get_action has the same name as the Button event handler in the view.
I have registeed the event in the method WDDOINIT of the view.
However I get an error as displayed bellow.
Please can anyone help me to find out how to bring it to work correctly.