No Errata
Q: When Forceful Denial is played in response to a ploy with a chance of failure (or a degree of success), like Daylight Robbery or Healing Potion, can it be played after it has been determined that the ploy (or how much the ploy) has succeeded?
A: No, it must be played before the success or failure of that card is determined.
Q: Can I use Forceful Denial in response to a ploy played as a reaction?
A: Yes – the trigger for Forceful Denial is your opponent playing a ploy, which is a different trigger to the one they played their reaction against.