At this time, I’m afraid it isn’t quite possible to @mention someone via the API. You can create an update that looks like an “@mention”, using the same format for your update’s body as returned in the query. For example:
"<a class=\"user_mention_editor router\" href=\"https://{slug}.monday.com/users/{user-id-to-mention}-{user-profile-name}\" data-mention-type=\"User\" data-mention-id=\"{user-id-to-mention}\" target=\"_blank\" rel=\"noopener noreferrer\">@{User Name}</a>"
This will look like a proper @mention on the board:
However, this will not actually trigger a notification. In this case, I can only recommend getting the ID of the new update when making the API request, and then creating a notification related to this update via the “create_notification” mutation.
I realize this is extra work for you to develop the solution on your end, but I hope this helps clarify. At this time, it is still not possible to “@mention” someone when you post the update via API directly.
-Alex