In some ”late moments” when you tap Cancel in the app for a match or activity, you will see the message ”Contact the club to leave this match/activity”.
This is due to the automatic cancellation rules that clubs may have set up for their matches and activities. The club can cancel your spot from the match/activity, but in late moments, you as a player may not be able to do so yourself, since it may affect all the other participants being cancelled as well.