Custom system notification

I am using v 14 and I am trying to make a notification when delivery percentage in sales order is 80 or above but the notification not work
I added a new system notification and select the:
Doctype type as sales order
the Send Alert On is custom
and i wrote in condition : doc.per_delivered >= 80
i do not know what is the problem if anybody can help

Make sure you have added recipients.
Change Send Alert On to New

@Yamen_Zakhour thanks for replay but i added recipient and change the send alert on option to new but the notification did not appear

My bad, just noticed you are working on Delivery % of Sales Order.
The “New” Trigger will only send a notification once a new sales order has been created. However, there is no way the delivery percentage for a new document can be greater than 80, thus you are not receiving any notifications.

Instead of “New” change it to “Value Change” and choose “per_delivered” for the “Value Changed”