Hello Charlotte!
Thanks for getting in touch with us! Let me help you with that.
I’m not really familiar with how Duo works with your site, but I took a quick look at how it works and it seems that it could be the problem here.
Is there a way you could try disabling the two factor authentication until you finish the connection with Eventbrite and then enabling it back again? If yes, could you try to do so and let me know if it works?
When coming back, could you please share with us your system info by following this guide > https://theeventscalendar.com/knowledgebase/sharing-sys-info/ ? This way we can see if there is anything strange that might be involved too.
Let us know about it.
Thanks,
Victor