In many cases, the Eventbrite order confirmation email you received when you registered will be enough to prove a purchase. To find it, search your email inbox for "noreply@order.eventbrite.com". If you need a more formal receipt, invoice, or your order confirmation email resent, please contact the event organiser which can be found on the event listing or event ticket.
For more information, please visit this link: https://www.eventbrite.com/help/en-us/articles/123856/get-a-receipt-for-your-tickets/