You might have missed it, but there’s another check before the persuasion check in the guide, the check for “host social”. You might not have passed that check?
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)_/¯