If you declined notifications when installing the Ski Club app you can either:
visit Chats from the main menu of the app and it may ask you again; or
delete the app and re-install it to trigger the notification request again.
If you accepted notifications, but aren't seeing them:
make sure you are not in Do Not Disturb or any similar mode; and
notifications for the Ski Club app are not disabled in your phone's settings.
Otherwise, if you're still having trouble follow the steps above for 'if you declined notifications when installing the app'.