How can I set a longer prefix key?

[madorian]

It says "it's not a prefix key"

I'm trying to set

  (persp-mode-prefix-key (kbd "C-M-w p"))

I need to type it in a bit different?

[gcv]

That works for me in the :custom block of use-package. You need to use either that, the Customize UI, or (customize-set-variable 'persp-mode-prefix-key (kbd "C-M-w p")). How are you trying to set it?