If you want this code to be executed whenever the account_id changes, you can use the @api.onchange decorator. However, keep in mind that onchange methods are not stored in the database, they are mainly used for UI purposes.

Here’s an example of how you might use the @api.onchange decorator:

from odoo import api, models

class AccountMoveLine(models.Model):
    _inherit = 'account.move.line'

    @api.onchange('account_id')
    def _onchange_account_id(self):
        if self.move_id.move_type == 'out_invoice' and self.account_id.user_type_id.id == '1':
            so = self.env['sale.order'].search([('name','=',self.move_id.invoice_origin)])
            if so:
                custom = self.env['custom'].search([('name','=',so.origin)])
                if custom:
                    custom_account = self.env['ir.config_parameter'].sudo().get_param('custom_account')
                    if not custom_account:
                        raise UserError('Configure the custom account!')
                    self.account_id = int(custom_account)

This code will trigger whenever the account_id field is changed in the UI. If you want this logic to be applied every time a record is created or written to, regardless of whether it’s through the UI or not, you might want to override the create and write methods instead.

Remember to update the module after adding this code to apply the changes. If the function still isn’t triggering, there might be an issue with the conditions in your if statements. Make sure the conditions are being met when you’re testing the function.

Hope it helps.