This is even more complicated. There is no guarantee that the request will make it to the relay. So you might need to send it multiple times. If your post got ever broadcasted on other relays you will have to ask those as well. (effectively asking every single relay on the planet)

The last thing is, how they honor it. Do they unrecoverably delete the event, delete it only from the production database, flag is as hidden in the database... There is no way to tell.