Rails find order id on mailer

On a order mailer to find the order id i used order_id, but rails return a error, if i use params the same.

what's the way to get find the object id on a mailer?

def order_confirmation(order)
    order = Order.find(order_id)
    @user = order.buyer_id
    mail(to: @user.email, subject: 'Confirmação da Compra', &:html)
  end