Hi,To achieve your requirement of generating a sequence code for stock pickings only when their state changes to "done", you can override the button_validate() method of the stock.picking model. This method is called when the picking's state changes to "done". Here's how you can do it:from odoo import models, api

class StockPicking(models.Model):
    _inherit = 'stock.picking'

    def button_validate(self):
        # Call super to perform the default behavior
        res = super(StockPicking, self).button_validate()

        # Loop through the pickings
        for picking in self:
            # Check if the picking is in 'done' state
            if picking.state == 'done':
                # Generate sequence code if it's not already set
                if not picking.name and picking.picking_type_id.sequence_id:
                    picking.name = picking.picking_type_id.sequence_id.next_by_id()

        return res

Hope it helps