unknownError (error code 0): Unknown error

• iOS StoreKit 1: an SKError code the SDK does not map. The SKError mapping covers a fixed list, and anything else, including undocumented codes, falls through to unknownError.
• iOS StoreKit 2: a StoreKitError or Product.PurchaseError case that is newer than the SDK. The StoreKit mapping sends every unknown case here.
• Android: an exception that is not a network, security or signature failure becomes unknownError, and so does any Play Billing response code outside the known list (errors.kt).
• The backend answered with code 0, which the SDK reads as "we don't know what happened" (BackendErrorCode.swift).
• Flutter: PurchasesErrorHelper.getErrorCode returns unknownError when the platform error code is outside the enum's range.

• Do not grant access. Nothing in the error says the purchase succeeded.
• Do not retry automatically. Let the customer tap the button again, because an unknown failure may repeat.
• Show a neutral message such as "Something went wrong, please try again", and log the underlying error so you can classify it later.

// Swift
do {
  let result = try await Purchases.shared.purchase(package: package)
} catch let error as ErrorCode where error == .unknownError {
  // handle unknown error
}

// Kotlin
if (error.code == PurchasesErrorCode.UnknownError) { /* ... */ }

On RevenueDot: RevenueDot always answers failures with a JSON body that has a numeric code, so a server failure reaches the SDK as a backend error (unknownBackendError at worst), not as unknownError. See what RevenueDot's API errors mean.