Activity-watch-emacs mode does not work



i installed activity-watch-mode for emacs by instruction.

M-x install-package [Ret] activity-watch [Ret]

from melpa. I activate activity-watch-mode with

M-x global-activity-watch-mode

but it does not add a new pool and no new information to my running instance.

Any ideas?
Edit 1:
the messages buffer contained the following:

Error running timer ‘activity-watch--save’: (void-function json-encode) (14 times)


The emacs watcher is maintained by @pauldub, not sure how active he is on this forum but if he doesn’t answer here you can try to create an issue on GitHub.