Please read this article: https://waterspeed.crunch.help/en/how-to/how-to-setup-siri-shortcuts-to-start-stop-or-pause

NOTE: If Pause or Stop are not working on Watch, you can use:

- the 2 lateral buttons together: https://waterspeed.crunch.help/en/how-to-on-watch/how-to-use-lateral-buttons-to-pause-or-stop

- the Ultra Action button, if you have that device: https://waterspeed.crunch.help/en/how-to-on-watch/action-button-on-apple-watch-ultra