When you receive your sandbox account you will get access to 'partner hub'.
To configure your trigger go to settings/partner hub.
Please feel free to use our starting point code:
You can always edit partner properties by clicking on a partner name, and you can edit a provider key as well.
You can go to the job and set up a trigger. Then, when a candidate is be moved to that stage a partner event will be sent to the /webhook endpoint
In the terminal you can log how the payload looks:
Notice the webhook-data is the value picked by the user in the previous step.