RDM Verflare tooltip doesn't say what activates it.

[Ivtrix]

The reason Enchanted Redoublement and Verflare don't tell how to use it is because the Mana Stack mechanic doesn't require that you use Enchanted Redoublement at all. You can do the combo correctly (E.Riposte, E.Zwerchhau, E.Redoublement) or you can do it in any incorrect combination that you can afford with your black and white mana, such as

E.Riposte, E.Riposte, E.Riposte
E.Redoublement, E.Zwerchhau, E.Moulinet
E.Riposte, E.Moulinet, E.Zwerchhau

Of course non-combos like that do far less damage than a proper combo, but they are still something you can do. You just have to do any three Enchanted weaponskills other than E.Reprise. This is allowed because it's sometimes actually useful to switch to single target after one or two E.Moulinet, such as when a boss pops a group of adds but the boss is still targetable. In that case you might do the most damage with E.Moulinet, E.Moulinet, E.Riposte because the first two attacks killed the adds.

It’s funny this is kind of an extreme both ends of rdm cause yeah you can yolo whatever fucking melee abilities you want as long as you get 3 charges to finish the combo but at the same time there’s a high level theory where you can 3x zwer and get a melee combo out faster and only needing 45/45 mana, but the caveat is it’s way less potency so you only really do it based on kill times and if you can’t finish a standard combo before the boss dies.