Howdy Paul,
I would love to help you with this.
Did you know we actually have an extension you can download that does this for you? If you download, install and activate this plugin you will see the option “Carbon Copy the Organizer email when an order for tickets/RSVPs is approved, sharing the full tickets details.” in WP-Admin > Events > Settings > Tickets.
Plugin: tribe-snippet-email-organizer
The best way to do what you are doing is no via $_POST, but to do what that snippet does. It attaches it self to a relevant action, in this case ‘event_tickets_rsvp_tickets_generated’, and then uses the $order_id variable that action passes to retrieve the event and any of its details such as the venue. But perhaps just installing the plugin will be enough?
Did that help?
Cheers!
– Brook