The shortest answer to the question of what voluntary financial liability means is; It is an additional insurance coverage that secures material and physical damages that are not covered by traffic insurance and exceed the compulsory limits. Superhero insurance comes into play where compulsory traffic insurance is not sufficient.
Superhero insurance, which comes into play when compulsory traffic insurance is not enough. You were involved in a traffic accident and damaged the other party. Compulsory traffic insurance only covers a certain part of the damage. Unfortunately, this is not always enough. Voluntary Financial Liability (IMM) covers that insufficient part.