RSVP was a vertical version of Scrabble introduced by Selchow and Righter in 1958 and promoted as " 3-D Scrabble". Two players spelled words using cubical tiles with letters on an upright grid board.
RSVP was sold in the UK under the Spear's Games label as item #1051 (Copyright 1966 by Production and Marketing Company, 1968 J. W. Spear & Sons Ltd) with the how to play/rules printed inside the box lid.
The playing space is a dark blue vertical frame, held upright by two detachable black feet, with 11 x 11 square holes with 75 wooden block lettered playing pieces available to place within that frame. The letter blocks are similar to regular Scrabble tiles showing a large letter and a small number for their scoring point value (identical on their opposing faces). There are no 'blank' blocks.
From the introduction inside the box lid: