For both test and live modes, you need to set up Stripe Webhooks in the Stripe admin dashboard.
Create a webhook pointing to https://[YOURDOMAIN]/lib/stripe.callback.php
Stripe will give you a webhook signing secret, this will need to be entered into the Unicity Settings interface. There will be a different signing secret for the test and live modes.
The events you need to send to Unicity CMS depending on what modules you are using. For most uses (e.g. Donations), the following will apply.
When creating the webhook, under "Filter event" select "Select types to send" and tick the following items: