> For the complete documentation index, see [llms.txt](https://docs.onside.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.onside.io/sdk/products-and-subscriptions/subscriptions.md).

# Subscriptions

An auto-renewable **subscription** is an [`OnsideProduct`](/sdk/products-and-subscriptions/fetching-products.md) like any other — you [fetch](/sdk/products-and-subscriptions/fetching-products.md) it, [purchase](/sdk/purchasing/making-a-purchase.md) it, [restore](/sdk/purchasing/restoring-purchases.md) it, and [validate](/sdk/purchase-validation/purchase-validation.md) it through the exact same APIs as a consumable or non-consumable. What sets a subscription apart is a small set of subscription-only properties describing its **billing period**.

{% hint style="info" %}
**The OnsideKit subscription API is intentionally small.** Renewals, cancellations, upgrades, billing retries, and the subscription-management UI are handled by the **Onside app** and your backend — not by the SDK. In your app you only *fetch*, *display*, *sell*, *restore*, and *validate* subscriptions; everything on this page covers exactly that.
{% endhint %}

## Detecting a subscription

A product is a subscription when its `subscriptionPeriod` is non-`nil`. That single check distinguishes a subscription from a one-time product:

```swift
if let period = product.subscriptionPeriod {
    // Subscription — billed once every `period`.
} else {
    // One-time product (consumable or non-consumable).
}
```

## Subscription properties

These properties live on [`OnsideProduct`](/sdk/reference/models.md#onsideproduct). `subscriptionPeriod` and `subscriptionGroupIdentifier` are populated **only** for subscriptions and are `nil` on a one-time product. `price` is non-optional and present on every product; for a subscription it is the recurring per-period charge.

<table><thead><tr><th width="300">Property</th><th>Description</th></tr></thead><tbody><tr><td><code>subscriptionPeriod: OnsidePeriod?</code></td><td>The recurring billing period. Non-<code>nil</code> only for subscriptions — use it to detect one.</td></tr><tr><td><code>subscriptionGroupIdentifier: String?</code></td><td>The subscription group the product belongs to.</td></tr><tr><td><code>price: OnsidePrice</code></td><td>The product price. For a subscription, the amount charged each billing period.</td></tr></tbody></table>

## The pricing types

```swift
struct OnsidePrice {
    var value: Double
    var currencyCode: String   // ISO 4217, e.g. "EUR"
}

enum OnsidePeriod {
    case day(UInt)
    case week(UInt)
    case month(UInt)
    case year(UInt)
}
```

* `OnsidePrice` — a numeric amount plus an ISO-4217 currency code.
* `OnsidePeriod` — a unit with a count, e.g. `.month(1)` (monthly) or `.year(1)` (yearly).

## Displaying a subscription

Combine the recurring price with the period:

```swift
func describe(_ product: OnsideProduct) -> String {
    guard let period = product.subscriptionPeriod else {
        return format(product.price)   // one-time product
    }
    return "\(format(product.price)) / \(describe(period))"
}

func describe(_ period: OnsidePeriod) -> String {
    switch period {
    case .day(let n):   return n == 1 ? "day"   : "\(n) days"
    case .week(let n):  return n == 1 ? "week"  : "\(n) weeks"
    case .month(let n): return n == 1 ? "month" : "\(n) months"
    case .year(let n):  return n == 1 ? "year"  : "\(n) years"
    @unknown default:   return "period"
    }
}

func format(_ price: OnsidePrice) -> String {
    let formatter = NumberFormatter()
    formatter.numberStyle = .currency
    formatter.currencyCode = price.currencyCode
    return formatter.string(from: price.value as NSNumber) ?? "\(price.value) \(price.currencyCode)"
}
```

{% hint style="info" %}
`OnsidePeriod` is a resilient (non-frozen) enum — keep an `@unknown default` in every `switch` so your code stays forward-compatible with future cases. See [Threading & Object Lifetime](/sdk/core-concepts/threading-and-retention.md#switching-over-onsidekit-enums).
{% endhint %}

## Purchasing a subscription

Buying a subscription is identical to buying any other product: wrap it in an `OnsidePayment` and add it to the [payment queue](/sdk/core-concepts/payment-queue.md). The resulting transaction flows through your observer with the same states (`.purchasing`, `.purchased`, `.failed`).

```swift
let payment = OnsidePayment(product: subscription)
Onside.defaultPaymentQueue().add(payment, completion: nil)
```

See [Making a Purchase](/sdk/purchasing/making-a-purchase.md) for the full flow — processing the transaction, **finishing** it, and the storefront safety gate.

## Restoring a subscription

A subscription is restorable, just like a non-consumable. When the user reinstalls your app or switches devices, `restoreCompletedTransactions(completion:)` re-delivers it as a `.restored` transaction. See [Restoring Purchases](/sdk/purchasing/restoring-purchases.md).

A renewal can also arrive **unprompted**: the payment queue reconciles it from the server and delivers it to your observer like any other transaction, so process and finish it the same way. See [Transactions can appear without an explicit purchase](/sdk/core-concepts/payment-queue.md#transactions-can-appear-without-an-explicit-purchase).

## Validating a subscription

The authoritative subscription status — whether it is active, when the current period **expires**, and whether it was cancelled — lives on the server. Verify it from your backend through the [Merchant API](/sdk/purchase-validation/merchant-api.md): a subscription transaction carries an `expires_at` and a `product_type` of `"SUBSCRIPTION"`.

## Testing subscriptions locally

You can define subscriptions in a `.storekit` file and exercise the whole fetch → purchase → restore flow offline, with no backend. See [Local Testing with a .storekit File](/sdk/advanced-and-tooling/local-testing.md).


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