bookingpress_after_book_appointment

    add_action('bookingpress_after_book_appointment', 'bookingpress_after_book_appointment_func', 10, 3);
    function bookingpress_after_book_appointment_func($inserted_booking_id, $entry_id, $payment_gateway_data)
    {
        //$inserted_booking_id Appointment id
        //$entry_id entry id
        //$payment_gateway_data payment gateway data
    }