Seat Reservations Brussels, Amsterdam, London

Hello, I am trying to reserve seats to travel between Brussels and Amsterdam. Through the Eurail website I booked EUR 9303, which leaves at 7:52 am, but when I go to the seat reservation page it only shows me train EUR 9301, so I don't know how to make the reservation. Otherwise, I cannot find the trains EUR 9322 for the Amsterdam-Brussels route and ES 9125 for the Brussels-London route. Could you tell me what these situations are due to or where I should make reservations? Thank you so much.