Hi Monika,
Thanks for reaching out!
I tried recreating the issue on my end with the information you’re using but was not able to do so. Is this the first time you’ve tried sending events to Eventbrite, or have you been able to successfully do this before?
The first thing I would recommend is to update to the current versions of WordPress (4.8) as well as The Events Calendar (4.5.6) and Eventbrite Tickets (4.4.5) and see if that solves the issue for you. If not, the next step would be testing for conflicts. If you don’t want to do this on your live site, I would recommend using a plugin like WP Staging that will let you create a quick copy of your live site that you can use for testing.
Let me know how that goes!
Thanks,
Jennifer