There's an error I can't fix

You really need to explain the entire interactive process, a use case if you will.

You must clarify:

  • What WP_Oku and Wp_Not_2 are and should do.
  • Are you creating the widgets in the level BP or is there a BP per paper?
  • In a matter of fact, what is a paper and a card?
  • How many papers are there?
  • How should everything work.

The right solution depends on the functional requirements.