I am working on a product team for Eventbrite.
Unfortunately, dynamic fields are not what we created for confirmation by email. I will be sure that this will be added to our function request queue.
Here's more information on what an order confirmation email looks like: http://help.eventbrite.com/customer/portal/articles/426236-order-confirmation-customization
As you can see, Eventbrite automatically sends an email with the name of the event and the order number. On this confirmation email, we allow you to add custom text, but we do not allow bulk customization. This is done by design, because we found that with too much customization, the format was broken, and the participants could not accurately decipher the important information from the confirmation.
Hope this helps!
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