Premium Economy seats are not being sold on flights between Singapore and Jakarta, however I was able to select one of them during online check-in. For what’s it worth, the flight in Economy was not fully booked and I purchased ticket in subclass H. Strangely no orange pillow provided during the flight.
Flight: Singapore Airlines SQ962
Route: Singapore (SIN) – Jakarta (CGK)
Aircraft: Airbus A350-900
More review: https://www.jambukebalik.com