[JS-SDK] Trying to upgrade a subscription with a prorata charge, but still can't understand how

[eLiosh]

Hi to all,

I'm trying to solve an "upgrade your current plan" problem.

I've created two plan for the same product: both have a duration of 1 month, one has a price of 15€ and the second one has a price of 40€.

If a user buyed the cheaper one, I'd like to let him pay the difference if he tries to buy the expensive one.

I've tried with this js-code: 

revise_obj.plan = {};
revise_obj.plan.billing_cycles = [
  {
    sequence: 1,
    total_cycles: 1,
    tenure_type: "TRIAL",
    frequency: {
      interval_unit: "DAY",
      interval_count: 1
    },
    pricing_scheme: {
      fixed_price: {
        value: selector.dataset.prorata,
        currency_code: "EUR",
      },
    },
  },
  {
    sequence: 2,
    total_cycles: 0,
    tenure_type: "REGULAR",
    frequency: {
      interval_unit: "MONTH",
      interval_count: 1
    },
    pricing_scheme: {
      fixed_price: {
        value: selector.dataset.price,
        currency_code: "EUR",
      },
    },
  }
];
return actions.subscription.revise(settings.megapro.subscription_id, revise_obj);

But I have this error in developer console: 

Error: Revise Subscription Api HTTP-422 response: error:

{
    "name": "UNPROCESSABLE_ENTITY",
    "message": "The requested action could not be performed, semantically incorrect, or failed business validation.",
    "debug_id": "f4150769c579b",
    "details": [
        {
            "field": "/plan/billing_cycles/1/sequence",
            "value": "2",
            "location": "body",
            "issue": "INVALID_BILLING_CYCLE_SEQUENCE",
            "description": "The provided billing cycle sequence is not available."
        }
    ],
    "links": [
        {
            "href": "https://developer.paypal.com/docs/api/v1/billing/subscriptions#UNPROCESSABLE_ENTITY",
            "rel": "information_link",
            "method": "GET"
        }
    ]
}

I've tried also with a setup_fee, but without luck.

Do someone solved this problem ?