I’m using the stock web client of slrpnk.net (whatever version that is), and when I type @Emperor@feddit.uk … oh, wow, that worked. Strange. In the cases that failed me, I copy-pasted the user’s address. So apparently it must be typed out manually to trigger auto-complete. I see that the client just makes it a markdown hyperlink to your profile. That’s useful, but what’s more important is that the user get a notification. When i copy-paste the address (e.g. @Emperor@feddit.uk) there’s nothing to signal to me that the user was recognized and that they will actually be populated in the “mentions” field of the JSON record.