Yes. If you call the tagline, you spend the Prowess for it whether successful or not. This also extends to Feats as well. In Forest of Doors, if a resource is spent to do something it stays spent whether it was successful or not.
Do I still spend Prowess on combat abilities (such as a Power Strike) that do not successfully hit?
About the Author: Fractured Larp
Fractured is a “survival” LARP with dark fantasy and horrific elements presenting a diverse array of character possibilities. Our setting and rules system promote a game where disparate and often alien peoples are forced by circumstance to stand by one another for the purpose of continued survival. The setting is as mysterious and player-responsive as you make it.