While hosting the ball I wasn't able to persuade people to peace in spite of having high enough persuasion to hit the check? 80 eloquence + 85 leadership + 85 charisma + 35 manipulation + 60 poise + 105 insight is 450 exactly, so either the guide needs to be updated or the check isn't functioning as it should...
Viewing post in Bug Reports and Errors
From looking at the guide you get 7 "host social" just for hosting in the first place and then +2 (or 1, or 0, or -1) for each kingdom depending on your nation approval, and the total host social check is supposed to be 13 or higher - I don't have screenshots or exact number values or anything but four out of seven kingdoms were definitely at max approval (which should have meant +8) and I'm pretty sure all of them were past the halfway mark?
I also had 300+ likeability for the check beforehand, so ¯\_(ツ)_/¯