Something seems to be wrong with this type of quest lately.
Login get the quest click on the green tick to pay the troops the button disappears and nothing happens.
Workaround is to refresh and then the quest can be completed normally.
Happened with soldier and longbowman quests. According to wiki the names are Military Extension and The Play.
The quests to pay more than 1 type of troop seem to be unaffected.
