We've decided to give our Product Owners the ability to comment directly to Clients in Jira Service Management (JSM).
They have "Add Comment" and "Edit Own Comment" permission on the project and they are members of jira-servicedesk-users so that they have JSM licences.
Despite this, they are still not able to see the "Share with customer" button when they comment on JSM tickets.
What else do they need?
I haven't made them agents because they don't need any of the other agent capabilities, and nothing in the documentation (that I can find) says that you have to be an agent to comment, just that you need a licence.
