Hi,

The reason your automated action isn't triggering is that qty_available is a computed field (store=False), so Odoo's "On update" trigger only fires on direct ORM write() calls; which never happen on product.product during a POS sale. POS processes stock through stock.move internally, completely bypassing your automation.

The cleanest solution without custom development is to create an automated action on the stock.move model instead, with trigger set to "On Creation & Update", and the following filter:

state = done
AND location_dest_id.usage = customer
AND product_id.qty_available < 0

Then set the action to schedule an activity on the related product_id. This fires as soon as the POS order is validated and the move is confirmed.

If you prefer a simpler approach, a scheduled action (cron) every few minutes on product.product works reliably:

records = env['product.product'].search([('qty_available', '<', 0)])
for rec in records:
    rec.activity_schedule('mail.mail_activity_data_todo', summary='Negative stock: ' + rec.name)

Hope this helps!