BukkitAudience#openBook doesn't work on Paper 1.21

[Syrent]

I've created a simple test plugin using these versions of Adventure:

• adventure-api version 4.17.0
• adventure-text-minimessage version 4.17.0
• adventure-platform-bukkit version 4.3.3

I relocated net.kyori to org.sayandev.adventuretest.lib.net.kyori as shown here and ran the server using run-paper version 2.3.0 with Paper version 1.21.

However, when I try to open a book, nothing happens. Everything else, such as the action bar, messages, etc., works as expected.