Send prefix key to emacs does not work (`send-escape')

Hello, as the title I am trying to send the prefix key `C-t' to emacs
through `send-escape' (C-t t), but it doesn't go through to emacs. It
works on firefox however. What am I missing here?

stumpwm version is 24.11, emacs version 30.2, firefox 147.0.4

All the best!