curl --request POST \
  --url https://api.hyperline.co/v2/subscriptions/{id}/prepare-upgrade \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "plan_id": "plan_123456789",
  "apply_at": "2024-01-15T10:00:00Z"
}'

{
  "subscription": {
    "id": "sub_B6ClkdqNqVNBgY",
    "name": "Yearly subscription",
    "currency": "EUR",
    "status": "active",
    "purchase_order": "<string>",
    "customer_id": "cus_QalW2vTAdkR6IY",
    "plan_id": "plan_zHmjoDee4ZRmQV",
    "invoicing_entity_id": "ive_jerrb484RHn",
    "checkout_session_id": "<string>",
    "crm_opportunity_id": "<string>",
    "minimum_invoice_fee": 250,
    "commitment_interval": {
      "period": "years",
      "count": 1
    },
    "renew_automatically": true,
    "renew_for": {
      "period": "years",
      "count": 1
    },
    "activation_strategy": "checkout",
    "starts_at": "2024-12-20T16:04:11Z",
    "contract_start": "2024-01-15T00:00:00Z",
    "contract_end": "2025-01-15T00:00:00Z",
    "initial_billing_at": "2024-12-20T16:04:11Z",
    "paused_at": "2024-12-20T16:04:11Z",
    "reactivate_at": "2024-12-20T16:04:11Z",
    "cancel_at": "2024-12-20T16:04:11Z",
    "cancellation_strategy": "refund_prorata",
    "cancellation_amount": 123,
    "cancellation_reason": "<string>",
    "estimated_arr": 123,
    "current_period_started_at": "2024-12-20T16:04:11Z",
    "current_period_ends_at": "2024-12-20T16:04:11Z",
    "next_payment_at": "2024-12-20T16:04:11Z",
    "next_payment_amount": 123,
    "renews_at": "2024-12-20T16:04:11Z",
    "current_phase_id": "<string>",
    "properties": {},
    "custom_properties": {},
    "generate_document": true,
    "document_name": "<string>",
    "add_tax_to_document": true,
    "created_at": "2024-10-12T07:00:01.860Z",
    "updated_at": "2024-10-12T07:00:01.860Z",
    "products": [
      {
        "id": "itm_FJKlqUb8COXw55",
        "name": "Product name",
        "description": "A description of the product.",
        "description_display_interval_dates": true,
        "attached_at": "2024-01-15T00:00:00Z",
        "detached_at": "2024-04-15T00:00:00Z",
        "current_period_started_at": "2024-01-15T00:00:00Z",
        "current_period_ends_at": "2024-02-15T00:00:00Z",
        "next_payment_at": "2024-02-15T00:00:00Z",
        "payment_interval": {
          "period": "months",
          "count": 1
        },
        "payment_schedule": "start",
        "type": "flat_fee",
        "count": 1,
        "prices": [
          {
            "type": "fee",
            "id": "<string>",
            "amount": 123
          }
        ]
      }
    ],
    "coupons": [
      {
        "description": "<string>",
        "expiration_date": "2023-11-07T05:31:56Z",
        "redemption_limit": 123,
        "created_at": "2024-12-20T16:04:11Z",
        "type": "amount",
        "discount_amount": 2000,
        "currency": "EUR",
        "id": "cou_DKL4Xcb5VSa8CQ",
        "promotion_code_id": "<string>",
        "name": "Partner discount",
        "subscription_coupon_id": "coos_d9pVekhjoGppuX",
        "repeat": "forever",
        "product_ids": [
          "itm_FJKlqUb8COXw55"
        ],
        "apply_at": "2023-11-07T05:31:56Z",
        "expires_at": "2023-11-07T05:31:56Z"
      }
    ],
    "phases": [
      {
        "id": "sup_1FoLfIQ5VOMbXf",
        "type": "standard",
        "status": "pending",
        "order": 0,
        "activation_strategy": "manual",
        "end_strategy": "duration",
        "duration": {
          "count": 1,
          "period": "years"
        },
        "billing_date_setting": "phase_start",
        "initial_billing_at": "2023-11-07T05:31:56Z",
        "starts_at": "2023-11-07T05:31:56Z",
        "ends_at": "2023-11-07T05:31:56Z",
        "billing_cycle_alignment": "anniversary",
        "transition_calculation_method": "prorata",
        "transition_invoicing_schedule": "immediately",
        "products": [
          {
            "id": "itm_FJKlqUb8COXw55",
            "name": "Product name",
            "description": "A description of the product.",
            "description_display_interval_dates": true,
            "attached_at": "2024-01-15T00:00:00Z",
            "detached_at": "2024-04-15T00:00:00Z",
            "current_period_started_at": "2024-01-15T00:00:00Z",
            "current_period_ends_at": "2024-02-15T00:00:00Z",
            "next_payment_at": "2024-02-15T00:00:00Z",
            "payment_interval": {
              "period": "months",
              "count": 1
            },
            "payment_schedule": "start",
            "type": "flat_fee",
            "count": 1,
            "prices": [
              {
                "type": "fee",
                "id": "<string>",
                "amount": 123
              }
            ]
          }
        ],
        "coupons": [
          {
            "description": "<string>",
            "expiration_date": "2023-11-07T05:31:56Z",
            "redemption_limit": 123,
            "created_at": "2024-12-20T16:04:11Z",
            "type": "amount",
            "discount_amount": 2000,
            "currency": "EUR",
            "id": "cou_DKL4Xcb5VSa8CQ",
            "promotion_code_id": "<string>",
            "name": "Partner discount",
            "subscription_coupon_id": "coos_d9pVekhjoGppuX",
            "repeat": "forever",
            "product_ids": [
              "itm_FJKlqUb8COXw55"
            ],
            "apply_at": "2023-11-07T05:31:56Z",
            "expires_at": "2023-11-07T05:31:56Z"
          }
        ],
        "created_at": "2024-10-12T07:00:01.860Z",
        "updated_at": "2024-10-12T07:00:01.860Z"
      }
    ],
    "quote": {
      "id": "quo_38YwqvItBH3d8a",
      "status": "signed"
    },
    "plan": {
      "id": "plan_zHmjoDee4ZRmQV",
      "name": "My example plan"
    },
    "checkout_session": {
      "id": "che_hEUPdVG7IgjpW1",
      "status": "opened",
      "available_payment_methods": [
        "card"
      ],
      "redirect_url": "https://app.hyperline.co/callback/checkout",
      "send_to": {
        "email": "josh@alpeak.com",
        "message": "<string>"
      },
      "url": "https://billing.hyperline.co/checkout/che_hEUPdVG7IgjpW1"
    },
    "payment_method_type": "card",
    "payment_method": {
      "id": "pm_1xMpj5bwRqN7LM",
      "status": "active",
      "type": "card",
      "last_4_digits": 2718,
      "expiration_date": "2027-11",
      "brand": "visa"
    },
    "generate_draft_invoices": true,
    "contract_terms": {
      "status": "active",
      "activation_strategy": "start_date",
      "end_strategy": "duration",
      "starts_at": "2024-12-31T23:00:00.000Z",
      "ends_at": "2025-06-30T21:59:59.999Z",
      "duration": {
        "count": 6,
        "period": "months"
      },
      "renew_automatically": true,
      "renew_for_duration": {
        "count": 1,
        "period": "years"
      },
      "current_period_started_at": "2025-06-30T22:00:00.000Z",
      "current_period_ends_at": "2026-06-30T21:59:59.999Z"
    }
  },
  "line_items": [
    {
      "product_id": "prod_123456789",
      "product_name": "Premium Plan",
      "amount": 5000,
      "usage": 123,
      "period_start": "2024-01-01T00:00:00Z",
      "period_end": "2024-01-31T23:59:59Z"
    }
  ]
}