I try to move a message sending from grok style to confiigure.zcml with a subscriber but that doesn't work as decribed in the Plone 5 developer documentation. I had already this function in my Dexterity object:
But there seemed to be no event fired up once a new file is added to the eupcenter folder. I never get a message in the shell (debug mode with Printing Host).
My guess is that your handler should be for IEUpProject, not IEUpCenter.
AFAIK IObjectAddedEvent is registered for the interface of the object that will be added, not the interface of the container to which the object is added.