That means what it says. You'll need to shorten that invalid author name to sync.

I encountered an issue while using Zotero. One of my references has a creator name field that's too long ("on behalf of the American Heart Association Exerci..."), preventing it from syncing. I've tried to delete the authors' names and title. The problem still persists. Could you please assist me in resolving this? I'm using Zotero version 7. Let me know if you need any more details.

@Pam200103: If you're getting that message, you still have an item with that creator. Note that it could be in the trash.