Strava Webhook API

I require the last leg of development for a a strava to caspio integration. All the work is done with regards to the API to this point, we are battling with the API subscription to Strava. Once this is done, strava will push the information to us for athletes who have subscribed to our services once they are finished with an activity.

https://developers.strava.com/docs/webhooks/

Above is a link to the information on how to do it with strava, we cannot get it working though. We are are stuck at the subscription stage.