"For all those who are not subjects belonging to the exclusion and exemption conditions, for the year 2025, the advance booking incentive has been introduced which provides for the payment of €5.00 only for those who pay the Access Fee within the fourth last day (inclusive) before the day of access. Otherwise, for those who pay the Access Fee in the 3 days before the day of access, the amount is equal to €10.00."
Source: https://cda.ve.it/en/
There is also an EuroNews article about it.
Differing prices for a public fee - no better service, no better offering: What is your opinion about it?