Currently, @mentions are only supported with the Ninja Forms add-on.

Each service supports @mentions slightly differently.

Slack

Slack supports @mentions exactly how you would expect it to work, by using the @ symbol followed by their username in Slack. For example, @daniel.

Discord

Discord’s support for @mentions works slightly differently. Instead of being able to use @username to mention someone, you have to use their Discord User ID, which is a number. You can find that number by typing \@username into one of your Discord channels, which will return something like <@970096885763898244>. So, to @mention that user, you will have to use @970096885763898244.