Getting @ mentions to work for Slack notification button

I am trying to create a Slack reminder button in a document that posts a message to a channel asking the task assignee for an update.

After installing the Slack pack I pulled in the users table for my channel. Then in my tasks table I changed the assignee column to a lookup column linked to the Slack users table. As the text for my reminder button I am using the following formula: concatenate(“Hey @”,thisRow.Asignee," could you update me on “,thisRow.Task,”. Thanks!"). The message posts to the channel successfully but only as text without actually tagging the user.

I was wondering if this can be done and if so how I can change my formula to make it work.