Assume the following situation: In a high-class (high enough for a video challenge system being in place) volleyball game an attack hit goes out of bounds and the referee assigns the point to the defending team. However, the attacking team thinks they have seen the block touching the ball and call a video challenge. When reviewing the video replay, the referee does not find a ball touch by the block, but it shows a touch of the net by one of the blocking players, so it would indeed be a point for the attacking team.
My question is now, what are the rules of such a challenge? Must the challenging team specify which type of fault they want to have reviewed (such as "block touched the ball") or is it enough to just challenge based on "during this action, we think that the situation was different from what the referee decided" and then just the whole situation is reviewed in the video material? And if the former is the case, is the referee obliged to give the challenge to the challenging team if they cannot confirm the reason for the challenge but finds a different fault that would change the original decision – such as the net violation in my example situation above?
Additional clarification: Since the video challenge is obviously not part of the official FIVB rules, let's restrict this question to international tournaments directly organized by the FIVB, i.e. World Cups and World League/World Grand Prix competitions.