Hello,
Add wait time after cast, and try to turnin manually the quest with runcode step:
if (wManager.Wow.Helpers.Quest.HasQuest(40643) &&
wManager.Wow.Bot.Tasks.GoToTask.ToPositionAndIntecractWithNpc(new Vector3(8001, -2680, 512), 101064))
{
wManager.Wow.Helpers.Quest.CompleteQuest();
}