docs: add appAccountToken UUID format requirement

- Update request-purchase.md with UUID format requirement and examples
- Update types.md with UUID format note
- Update purchases.md guide with UUID requirement

Refs hyochan/expo-iap#128

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

Author: hyochan

docs/docs/api/methods/request-purchase.md

@@ -62,7 +62,7 @@ class RequestPurchase {
 class RequestPurchaseIOS {
   final String sku;                    // Product ID
   final int? quantity;                 // Quantity (for consumables)
-  final String? appAccountToken;       // User identifier
+  final String? appAccountToken;       // User identifier (must be UUID format)
   final Map<String, dynamic>? withOffer; // Promotional offer
   final String? advancedCommerceData; // Attribution data (iOS 15+)
 }
@@ -102,7 +102,7 @@ await FlutterInappPurchase.instance.requestPurchase(
   RequestPurchaseProps.inApp((
     apple: RequestPurchaseIosProps(
       sku: 'com.example.premium',
-      appAccountToken: userId, // Your user ID
+      appAccountToken: userId, // Must be UUID format (e.g., '550e8400-e29b-41d4-a716-446655440000')
     ),
     google: RequestPurchaseAndroidProps(
       skus: ['com.example.premium'],
@@ -180,7 +180,7 @@ class PurchaseService {
           RequestPurchaseProps.subs((
             apple: RequestPurchaseIosProps(
               sku: productId,
-              appAccountToken: userId,
+              appAccountToken: userId, // Must be UUID format
             ),
             google: RequestPurchaseAndroidProps(
               skus: [productId],
@@ -193,7 +193,7 @@ class PurchaseService {
           RequestPurchaseProps.inApp((
             apple: RequestPurchaseIosProps(
               sku: productId,
-              appAccountToken: userId,
+              appAccountToken: userId, // Must be UUID format
             ),
             google: RequestPurchaseAndroidProps(
               skus: [productId],

docs/docs/api/types.md

@@ -37,7 +37,7 @@ iOS-specific purchase parameters.
 class RequestPurchaseIOS {
   final String sku;                                                   // Product SKU
   final bool? andDangerouslyFinishTransactionAutomaticallyIOS;       // Auto-finish transaction
-  final String? appAccountToken;                                      // App account token
+  final String? appAccountToken;                                      // App account token (must be UUID format)
   final int? quantity;                                               // Purchase quantity
   final PaymentDiscount? withOffer;                                  // Promotional offer
 

docs/docs/guides/purchases.md

@@ -78,22 +78,24 @@ Using the builder pattern (recommended):
 await iap.requestPurchaseWithBuilder(
   build: (builder) {
     builder.ios.sku = 'product_id';
-    builder.ios.appAccountToken = userId;
+    builder.ios.appAccountToken = userId; // Must be UUID format
     builder.android.skus = ['product_id'];
     builder.android.obfuscatedAccountIdAndroid = userId;
     builder.type = ProductQueryType.InApp;
   },
 );
 ```
 
+> **⚠️ Important:** The `appAccountToken` must be a valid UUID format (e.g., `550e8400-e29b-41d4-a716-446655440000`). If a non-UUID value is provided, Apple will silently return `null` for this field in the purchase response. See [OpenIAP Request Types](https://openiap.dev/docs/types/request) for details.
+
 Or using props directly:
 
 ```dart
 await iap.requestPurchase(
   RequestPurchaseProps.inApp((
     apple: RequestPurchaseIosProps(
       sku: 'product_id',
-      appAccountToken: userId,
+      appAccountToken: userId, // Must be UUID format
     ),
     google: RequestPurchaseAndroidProps(
       skus: ['product_id'],