David Kimura PRO said almost 3 years ago on Payment Gateway Basics with Stripe :
They may have changed the api again. I stopped using their Stripe Payments solution and prefer the Stripe Checkout. But, if this is the route you want to go. see this resource of their latest API docs. https://stripe.com/docs/api/subscriptions/create

Stripe::Subscription.create({
  customer: 'CUSTOMER_NUMBER',
  items: [
    {price: 'price_1aUj7wdGdu1FeVHa2AEY0Rph'},
  ],
})