margin and margin_percent fields are inside the sale order line (o2m field of sale order). So you will have to traverse to these fields in the xpath as shown in the below code.

    record model="ir.ui.view" id="sale_margin_sale_order_line_form"
        field name="name">sale.order.line.tree.margin.view.form/field
        field name="model">sale.order/field
        field name="inherit_id" ref="sale_margin.sale_margin_sale_order_line_form"/
        field name="arch" type="xml">
           xpath expr="//field[@name='order_line']/tree//field[@name='margin']" position="attributes"
               attribute name="invisible">1 /attribute
           /xpath
           xpath expr="//field[@name='order_line']/tree//field[@name='margin_percent']" position="attributes"
               attribute name="invisible">1 /attribute
           /xpath
        /field
    /record

Hi,

The margin and margin_percent fields are optional. You can hide them by disabling the fields using the toggle button in the sale order line.

Alternatively, you can also do it through the code:

<record model="ir.ui.view" id="sale_margin_sale_order_line_form">
<field name="name">sale.order.line.tree.margin.view.form</field>
<field name="model">sale.order</field>
        <field name="inherit_id" ref="sale.view_order_form"/>
        <field name="arch" type="xml">
<xpath expr="//field[@name='order_line']/tree//field[@name='margin']" position="attributes">
<attribute name="column_invisible">1</attribute>
            </xpath>
<xpath expr="//field[@name='order_line']/tree//field[@name='margin_percent']" position="attributes">
<attribute name="column_invisible">1</attribute>
            </xpath>
        </field>
    </record>

Make sure to add 'sale_margin' to the depends of your manifest file.

Hope it helps

Hi,

You should inherit sale.order instead of sale.order.line.

Please check below screenshot :