I am trying to get the quantity of boxes that i deliver, i get it when i use the sale module since i get access to the product_packaging_id value but i don't in the pos therefore if i try to get the delivery slip i get nothing in the number of boxes, i was trying to create a module in order to bring the product_packaging_id and product_packaging_qty in the pos module here is my code:
model: pos_packing.py : 
from odoo import models, fields

class PosOrderLineCustom(models.Model):    _inherit = 'pos.order.line'
    product_packaging_id = fields.Many2one(        comodel_name='product.packaging',        string="Packaging"    )
    product_packaging_qty = fields.Float(        string="Packaging Quantity"    )

and here is my view: pos_packing_view.xml:


            point_of_sale.view_pos_pos_form.custom        pos.order.line                                                                                                                                                                                                                                                                                                                            



and some how i am getting an error and it's not working if somebody could help i would appratiate it. Thank you!