I'm a Odoo v.13 CE user (not developer). I have a custom module that have many bugs, I'm trying to understand how fix bug, but I don't find solution.

Module, by barcode scanning in a custom field, add product line in Order with Product, Description, Qty, Unit price, and taxes. If same product barcode is scanned more time, is increase quantity in same product line.   Bugs are: 

1. In Purchase order, is not call correct Price_unit of supplier selected. It apply price 0 always.

2. In Sale order, is not call correct Price_unit of Pricelist selected, It apply default list_price always.

Please, someone can help me to fix this, and say me correct code to add? I'm not a developer, I don't know nothing about code and programming.

Thanks

----------Purchase Order code

def _add_product(self, product, qty, price):
        """Add line or update qty and price based on barcode."""
        corresponding_line = self.order_line.filtered(lambda r: r.product_id.id == product.id)        
        taxes = product.supplier_taxes_id.filtered(lambda t: t.company_id.id == self.company_id.id)
        taxes_ids = taxes.ids
        if corresponding_line:
            corresponding_line[0].product_qty += float(qty)
            corresponding_line[0].price_unit = float(price) or product.price      
            if self.partner_id and self.fiscal_position_id:
               taxes_ids = self.fiscal_position_id.map_tax(taxes, product, self.partner_id).ids
        else:
            self.order_line += self.order_line.new({
                'product_id': product.id,
                'product_qty': qty,
                'date_planned': fields.Datetime.to_string(datetime.datetime.now() - dateutil.relativedelta.relativedelta(months=1)),
                'name': product.name,
                'product_uom': product.uom_id.id,
                'price_unit': float(price) or product.price,         
                'taxes_id': [(6, 0, taxes_ids)],
            })
        return True

----------Sale Order code

def _add_product(self, product, qty, price):
        """Add line or update qty and price based on barcode."""
        corresponding_line = self.order_line.filtered(lambda r: r.product_id.id == product.id)
        taxes = product.taxes_id.filtered(lambda t: t.company_id.id == self.company_id.id)
        taxes_ids = taxes.ids        
        if corresponding_line:
            corresponding_line[0].product_uom_qty += float(qty)
            corresponding_line[0].price_unit = float(price) or product.list_price
            if self.partner_id and self.fiscal_position_id:
               taxes_ids = self.fiscal_position_id.map_tax(taxes, product, self.partner_id).ids
        else:
            self.order_line += self.order_line.new({
                'product_id': product.id,
                'product_uom_qty': qty,
                'name': product.name,
                'product_uom': product.uom_id.id,
                'price_unit': float(price) or product.list_price,
                'tax_id': [(6, 0, taxes_ids)],              
            })
            
        return True