remnant1930 No problem, you can travel with this Arcobaleno ticket, but this ticket is not valid in the Eurocity trains, you can use only regional trains. Please note that it is valid only 4 hours from 15:31 to 19:31. If you are earlier or later in Chiasso and you cannot make the entire trip Chiasso - Milano in the indicated period, you have to cancel this ticket before 15:31 and buy a new one.
If you want to take an Eurocity train between Chiasso and Milano, you should buy a ticket on Trenitalia.com or in Trenitalia app, but it is more expensive.
