Using Railpass in Italy and can't make reservations through the app rail planner

Bought the France-Italy pass with 6 travel days. Tried booking reservations for high speed and night trains but gets message invalid passholder number. My itinerary is:1June Nice, France to Milan on an 8:15am TGV train and need to reserve; 3June Milan to Florence; 5Jun Florence to Naples can or should I get night train and need to reserve?; 7Jun Pompei -Palermo Sicily need to reserve night train; 8Jun Palermo to Rome - need to arrive in Rome by 6am of June 9th. Is there a night train which allows me to use the pass?
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