Hi @dnewton,
Could you please share a screenshot of your flow's configuration?
Could you please show a bit more about your error message?
Further, could you please share a bit more about your SharePoint list?
I have made a test on my side and don't have the issue that you mentioned. My flow's configuration as below:
The flow works successfully as below:

Please check if the email address that you filled within Person or group field of "Create item" action is existed in your Office 365 organization.
Best regards,
Kris