ep3_join_faction_war_effect

ep3_join_faction_war_effect = {
	# Use hook/pay gold
	scope:actor = {
		if = {
			limit = {
				scope:hook = yes
				has_hook = scope:recipient
			}
			use_hook = scope:recipient
		}
		if = {
			limit = { scope:gold = yes }
			pay_short_term_gold = {
				gold = scope:actor.medium_gold_value
				target = scope:recipient
			}
		}
	}
	# Gain some influence
	scope:recipient = {
		change_influence = 75
		# Remove from existing faction if swapping
		if = {
			limit = { exists = joined_faction }
			leave_faction = joined_faction
		}
		if = {
			limit = { target_is_liege_or_above = scope:secondary_recipient }
			add_faction_cooldown_effect = { YEARS = 5 }
		}
		remove_character_flag = under_offer_join_faction_war_flag
	}
	scope:actor.joined_faction.faction_war = {
		if = {
			limit = { is_defender = scope:actor }
			add_defender = scope:recipient
		}
		else = { add_attacker = scope:recipient }
	}
}

As written in game/common/scripted_effects/07_dlc_ep3_scripted_effects.txt.