I have asked this question previously but I'm asking again to get a bump because I haven't gotten an answer yet. Here is the old question Finding user names to bulk upload issues via CSV (atlassian.com)
To summarise, I can't bulk upload because my project requires a product owner field to be mapped in a bulk upload and no names that I am putting in are being recognised. (We have just transistioned to new jira) I have tried the following:
1) Using people's email addresses eg johnsmith@microsoft.com
2) Searching in the old Jira for user names and using those eg josmit
3) Using people's names as they appear in Jira eg John Smith
4) Using people's domain names without the email address eg josmith
5) Trying different people eg: project owner, myself, another random person (all of which I can assign as the product owner to an individual issue outside of a bulk upload
Please help! 
