Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
Train Travel Discounts (Promo Tickets)
If you book Intercidades or Alfa Pendular trains at least 5 to 8 days in advance, you can get "Promo" tickets with discounts of up to 65%. A trip from Lisbon to Porto can cost as little as €10 instead of €30.
These tickets are non-refundable and tied to a specific time, but you can change the date once. Always book via the CP App or website, as ticket counters often sell full-price fares unless you specifically ask for promos.