Where to find username for invited sharer?

Thank you for that information. It's unfortunate that https://docs.aws.amazon.com/workdocs/latest/userguide/share-invite.html begins with this: 'You can invite users and groups to share a folder or file, within or outside your organization.' Given what you have just told me, AWS doesn't do what I want so I'll have to find a different solution.

Thanks for sharing the link to 'Sharing by invitation' document. This workflow is a bit different from 'Sharing a link' workflow that you originally asked about.

If you are using 'Sharing by invitation' to share the folder, that should work. Please note point #3 from that document under 'To invite people to share a folder or file' section:

" To invite people in your organizaton, in the Invite specific people box, enter the name of the person or group with whom you want to share, then select the desired name from the list of results.

—OR—

To invite people outside your organization, enter the email address of the person or group with whom you want to share. When you finish, the address appears in a pop-up. Select that pop-up to add the address to your list of users.

Note Your Amazon WorkDocs administrator has to authorize you to share files outside your organization. "