class PharmacySettings(models.TransientModel):
    _inherit = 'res.config.settings'

    product_group = fields.Many2one('product.group', string='Product Group')

    def set_values(self):
        res = super(PharmacySettings, self).set_values()
        self.env['ir.config_parameter'].set_param('custom_pharmacy_invoice_view.product_group', self.product_group)
        return res

    @api.model
    def get_values(self):
        res = super(PharmacySettings, self).get_values()
        ICPsudo = self.env['ir.config_parameter'].sudo()
        groups = ICPsudo.get_param('custom_pharmacy_invoice_view.product_group')
        res.update(
            product_group=groups

        )
        print(res)

When i wnat to save selection field value the this error occured:

psycopg2.errors.InvalidTextRepresentation: invalid input syntax for integer: "product.group(1,)"
LINE 1: ...FROM "product_group" WHERE "product_group".id IN ('product.g...

How can I solve it Please help me