I want to create orders from backend pos. So, I made button CREATE in pos.order visible. But when clicking on button , I got this error :

The operation cannot be completed:

- Create/update: a mandatory field is not set.

- Delete: another model requires the record being deleted. If possible, archive it instead.

Model: Point of Sale Orders (pos.order), Field: Returned (amount_return)

Here is my code:

//.xml

<record id="view_pos_order_create_extend" model="ir.ui.view">

        <field name="name">view_pos_order_create_extend</field>

        <field name="model">pos.order</field>

        <field name="inherit_id" ref="point_of_sale.view_pos_order_tree"/>

        <field name="arch" type="xml">

             <xpath expr="//tree" position="attributes">

                 <attribute name="create">1</attribute>

            </xpath>

        </field>

    </record>

//.py

 class PosOrderExtend(models.Model):

    _inherit = "pos.order"

    _description = "Point of Sale Orders"

    _order = "id desc"

      @api.onchange('payment_ids', 'lines', 'partner_id')

        def _onchange_amount_all(self):

            for order in self:

                currency = self.env.company.currency_id

                if self.partner_id.property_product_pricelist.currency_id:

                    currency = self.partner_id.property_product_pricelist.currency_id

                order.amount_paid = sum(payment.amount for payment in order.payment_ids)

                order.amount_return = sum(payment.amount < 0 and payment.amount or 0 for payment in order.payment_ids)

                order.amount_tax = currency.round(

                    sum(self._amount_line_tax(line, order.fiscal_position_id) for line in order.lines))

                amount_untaxed = currency.round(sum(line.price_subtotal for line in order.lines))

                order.amount_total = order.amount_tax + amount_untaxed

What's wrong please? How can I fix it ? Thanks.