I want to assign the tax_id from the product in the sale.order to my new field.

Here I have the screenshots:

Like in the screenshots I want to add the +8.0 UST directly in the tax field .

my code looks like this:

tax_line_ids = fields.Many2many('account.tax', string='Taxes', domain=['|', ('active', '=', False), ('active', '=', True)])



@api.onchange('order_line')
def _onchange_order_line(self):
    for line in self.order_line:

        if self.tax_line_ids.id == line.tax_id.id:
            return 0
        else:
            self.tax_line_ids.id = line.tax_id.id

But I get an error when I try to do this: self.tax_line_ids.id = line.tax_id.id

It should add the new TAX to the new field "tax_line_ids"

I get this error:

line 22, in _onchange_order_line
    self.tax_line_ids.id = line.tax_id.id
  File "/odoo10/odoo10-server/odoo/fields.py", line 2439, in __set__
    raise TypeError("field 'id' cannot be assigned")
TypeError: field 'id' cannot be assigned

I want to thank you for the incoming help.

Thank you