Y/N universe prompt in WEBI

Created a simple universe Y/N prompt and used it in a universe class filter to include or exclude certain records based on Y/N prompt using case statement. Just looking for the discrete Y/N return from the prompt to the universe to work the filter - not tied directly to any specific dimension. How to add to WEBI query panel?
Normally, a @prompt in a derived table will automatically show up as a prompt at webi runtime with no config in query panel. However, using the @prompt in a class filter doesn’t show up automatically as a prompt? Solution?

to create an independent prompt, you can use a dummy-FreehandSQL-statement in WebI as a
additional datasource which gives you only some input-prompt,
then join/merge this source with your other data, so the report will be filtered with the input-prompt.

Did you set the filter as mandatory?