stripe upgrade, prorate, and bill for proration instantly

gistfile1.txt

//create subscription
// $20 a month
curl https://api.stripe.com/v1/customers/cus_18nj91X8lMXyju/subscriptions    
	-u private key:    
	-d plan=gold

//change subscription - upgrade plan
//$40 a month
curl https://api.stripe.com/v1/customers/cus_18nj91X8lMXyju/subscriptions/sub_4HWcxqoS8wG7T3 \
   -u private key: \
   -d plan=platinum


//create an invoice this has two items (items get added automatically)
// an invoice item  - $20
// an invoice item  + $40 
curl https://api.stripe.com/v1/invoices \
   -u private key: \
   -d customer=cus_18nj91X8lMXyju
   
//invoice repsonse
{
  "date": 1403630438,
  "id": "in_4HWedjWJ6yHAOi",
  "period_start": 1403630314,
  "period_end": 1403630438,
  "lines": {
    "object": "list",
    "total_count": 2,
    "has_more": false,
    "url": "/v1/invoices/in_4HWedjWJ6yHAOi/lines",
    "data": [
      {
        "id": "ii_4HWeKdQstOPDJE",
        "object": "line_item",
        "type": "invoiceitem",
        "livemode": false,
        "amount": 4000,
        "currency": "usd",
        "proration": true,
        "period": {
          "start": 1403630422,
          "end": 1403630422
        },
        "quantity": null,
        "plan": null,
        "description": "Remaining time on Amazing Gold Plan after 24 Jun 2014",
        "metadata": {}
      },
      {
        "id": "ii_4HWe6lCsznwjVe",
        "object": "line_item",
        "type": "invoiceitem",
        "livemode": false,
        "amount": -2000,
        "currency": "usd",
        "proration": true,
        "period": {
          "start": 1403630422,
          "end": 1403630422
        },
        "quantity": null,
        "plan": null,
        "description": "Unused time on Amazing Gold Plan after 24 Jun 2014",
        "metadata": {}
      }
    ]
  },
  "subtotal": 2000,
  "total": 2000,
  "customer": "cus_18nj91X8lMXyju",
  "object": "invoice",
  "attempted": false,
  "closed": false,
  "paid": false,
  "livemode": false,
  "attempt_count": 0,
  "amount_due": 2000,
  "currency": "usd",
  "starting_balance": 0,
  "ending_balance": null,
  "next_payment_attempt": 1403634038,
  "webhooks_delivered_at": null,
  "charge": null,
  "discount": null,
  "application_fee": null,
  "subscription": null,
  "metadata": {},
  "statement_description": null,
  "description": null
   
 //then you'd have to charge the invoice