Validationが９月１５日(Not valid date)

“BUY TICKET”の画面で”Round Trip”を選択、”Departure Date”と”Return Date”を指定し９月１５日（Local time）に予約されたと推測します。したがって受信e-mailの翻訳の“Date of validity”は鉄道パスのValidation(Activation:適用開始日)と私なら解釈します。
水上バスの料金　1回券€7.5 ､1日券€20 ､2日券€30 ､3日券€40の15%か･･･
c/f
The perfect solution for your trips to Venice. Thanks to our partnership with ACTV, the Venice public transport company, if you travel with Italo to or from Venezia Santa Lucia you are granted a 15% discount off public transport tickets.
If you change your Italo ticket, you can redeem your discount within 2 years without making any change to your reservation and with no extra charges. You cannot cancel your reservation or change the type of service you have reserved.
Reserve your offer online on the Italotreno.it website. We’ll email you a code to redeem the discount at Vela ticket agencies and ACTV ticket machines.