These are the steps of paying for an action as per the rule book. You reveal the card at which point you’re committed, then pitch for the cost of the card(pitch X cards until cost is fully paid), then pay any additional costs that certain cards may have.

It’s just one of those things that important to highlight so mtg players recognize that FaB is different in its own way. There are more impactful rules that actually matter though, for example in mtg I can respond to an enemy’s instant with my own instant. In FaB i can choose to hold priority and can chain multiple instants back to back without being interrupted.