fix(apple): validate appAccountToken UUID format before purchase

Add validation that throws a clear error when appAccountToken is not
a valid UUID format. Apple silently returns null for non-UUID values,
which makes debugging difficult. This change fails fast with a
descriptive error message to help developers identify the issue.

Closes hyochan/expo-iap#128

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: hyochan

packages/apple/Sources/Helpers/StoreKitTypesBridge.swift

@@ -364,7 +364,19 @@ enum StoreKitTypesBridge {
         if let quantity = props.quantity, quantity > 1 {
             options.insert(.quantity(quantity))
         }
-        if let token = props.appAccountToken, let uuid = UUID(uuidString: token) {
+        if let token = props.appAccountToken {
+            guard let uuid = UUID(uuidString: token) else {
+                // Apple requires appAccountToken to be a valid UUID format.
+                // If a non-UUID value is provided, Apple silently returns null for this field.
+                // Fail fast with a clear error message so developers can identify the issue.
+                // Reference: https://openiap.dev/docs/types/request
+                OpenIapLog.error("❌ Invalid appAccountToken format: '\(token)'. Must be a valid UUID (e.g., '550e8400-e29b-41d4-a716-446655440000')")
+                throw PurchaseError.make(
+                    code: .developerError,
+                    productId: props.sku,
+                    message: "appAccountToken must be a valid UUID format (e.g., '550e8400-e29b-41d4-a716-446655440000'). Received: '\(token)'. Apple silently returns null for non-UUID values."
+                )
+            }
             options.insert(.appAccountToken(uuid))
         }
         if let offerInput = props.withOffer {