There should be two events you receive. The first (Reichstag at worms) starting in 1495 and the death date for it is 1505. You need to be Emperor which you already are, have 6 provinces, and not a badboy of 3.
These are the list of vassals needed.
AND = { #any combination of 3 of the 4 electors except Brandenburg
vassal = { country = BRA country = KOL }
relation = { country = KOL data = 100 }
vassal = { country = BRA country = MAI }
relation = { country = MAI data = 100 }
vassal = { country = BRA country = PFA }
relation = { country = PFA data = 100 }
}
AND = {
vassal = { country = BRA country = KOL }
relation = { country = KOL data = 100 }
vassal = { country = BRA country = MAI }
relation = { country = MAI data = 100 }
vassal = { country = BRA country = SAC }
relation = { country = SAC data = 100 }
}
AND = {
vassal = { country = BRA country = KOL }
relation = { country = KOL data = 100 }
vassal = { country = BRA country = PFA }
relation = { country = PFA data = 100 }
vassal = { country = BRA country = SAC }
relation = { country = SAC data = 100 }
}
AND = {
vassal = { country = BRA country = MAI }
relation = { country = MAI data = 100 }
vassal = { country = BRA country = PFA }
relation = { country = PFA data = 100 }
vassal = { country = BRA country = SAC }
relation = { country = SAC data = 100 }
}
The second event (Imperial Diet at Augsburg), and for this you need to be emperor, country size of 6, stability of 3, and not more than 3 badboy. The conditions for vassals are the same. The start date is 1500 and the death date is 1515. What year are you on?
Perhaps there are 6 certain provinces that you need?
Hopefully this helps.
