purchaseInvalidError (error code 4): Purchase invalid

• StoreKit 1: SKError.paymentInvalid (a payment parameter the App Store did not recognize) and unauthorizedRequestData (a property used without the required entitlement).
• StoreKit 2: StoreKitError.unsupported, which Apple documents as an operation that does not support the product.
• The SDK rejects a purchase quantity below 1 or above 10 before it reaches the store (PurchaseParams.swift).
• Android: Play Billing DEVELOPER_ERROR, which Google describes as improper API usage such as incorrect parameters (Google docs). Add-on products on a store other than Google Play also raise it.
• The backend answered 7105, 7106, or on iOS 7870, 8139 or 8140. On Android the web redemption codes 7849 and 7853 land here too.

• Do not retry the same call. A bad parameter fails the same way every time.
• Show a generic "purchase could not be started" message to the customer and send the details to your own logging.
• Do not grant access.

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

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

On RevenueDot: RevenueDot does not answer 7105 or 7106. A Google one-time purchase posted without product_ids gets code 7103, which the SDK reports as invalidReceiptError. RevenueDot does answer 7849 and 7853 for web redemption links, and on Android those arrive as this error.