Odoo version 10

I want to confirm sales order as soon as it gets created. For that, I'm trying below ruby command in irb but it always returns false and does not do any transition. 

irb(main):119:0> models.exec_workflow('admin', 1, '12345678', 'sale.order', 'confirm', 20)

=> false

I'm using the administrator user only which has all rights. I'm able to confirm the order using odoo web wizard.