Invoices are automatically sent to the users after their booking is success. So, you don't want to send it from anywhere. Also, the users can download their INVOICE at any time from their BOOKINGS menu in your website. You must add "My Bookings" menu in your website for this. Kindly refer "STEP 9: Configure User menus" section in yendif.com/joomla/events/getting-started.html
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