Why can't i mention someone in Jira?
In order to @ mention other users on Jira issues, you must have the Browse users and groups Global Permission. If you do not have this permission, when you type @ a list of users will not appear.
How do Jira mentions work?
To mention a person using autocomplete, type '@' in the editor, then start typing their name. Choose the person you want to mention from the list of suggestions. You can use autocomplete mentions in Jira Software Cloud as well.