Calendly can redirect someone to a page on your own domain after they book.
Set up the redirect URL in Calendly
In your event type, edit the booking
Click More Options
In the confirmation page settings choose Redirect to an external site
Turn on Pass event details to your redirected page so Calendly appends booking details to the end of your redirect URL.
Those details can include values such as the event name, invitee name, invitee email address, and UTM tags.
You can use that full redirected URL as the example URL in PixelFlow and map the parameters you want to send with the event.
Calendly requires a paid plan for redirect-based confirmation pages and for PixelFlow's webhook-based Calendly integration. If you want direct webhook tracking instead of URL Trigger tracking, see Trigger Events from Calendly Bookings.