Unfortunately it is not possible to tag your colleagues in Asana via Slack, my guess it that would be hard for Slack to distinct Asana mentions from Slack mentions. We already have a #productfeedback on this topic, so if you haven’t yet, I’d recommend upvoting this thread: Tagging in Asana via Slack. On my end, I’ll make sure to keep you posted when I have any update on this topic!