Hi Kelly,
21 digits, all numbers. The exact error message, which appears in a pink bar, is “The following Eventbrite error has occurred: Invalid user_key
This appears on the page in the ‘Import: Eventbrite’ of the plug-in.
I have checked and re-checked the user key entry, spent an hour educating the help desk at Eventbrite today (resulting in me being told it is impossible for any plug-in to import from Eventbrite into WP), un-installed the plug-in and re-installed, checked and re-checked.
The theme I am using is Responsive Free version.
I get the exact same error when creating an event in The Event Calendar and sending it to Eventbrite.
Question – does it matter if Eventbrite for WordPress is installed?