Let Harry forget about the gift, come in … but let Sirius do it!
As the Potterheads well know, the Red Flu is not exactly known for its reliability. Anyone hiding in the room could hear or even sabotage the conversation by sticking their head in the fireplace. In addition to this, it requires that the person you want to talk to is at home …
The moral is as fantastic and paradoxical as the world of Hogwarts itself: sometimes spoiling something is fixing it … and vice versa.