Merge pull request #279 from bizz84/feature/troubleshooting-iOS11-sandbox

Add link to iOS 11 beta sandbox forums

README.md

@@ -540,15 +540,19 @@ Note that the pre-registered in app purchases in the demo apps are for illustrat
 * [Apple - Restoring Purchased Products](https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/StoreKitGuide/Chapters/Restoring.html#//apple_ref/doc/uid/TP40008267-CH8-SW9)
 * [Apple - Testing In-App Purchase Products](https://developer.apple.com/library/content/documentation/LanguagesUtilities/Conceptual/iTunesConnectInAppPurchase_Guide/Chapters/TestingInAppPurchases.html): includes info on duration of subscriptions in sandbox mode
 * [objc.io - Receipt Validation](https://www.objc.io/issues/17-security/receipt-validation/)
-* [Apple TN 2413 - Why are my product identifiers being returned in the invalidProductIdentifiers array?](https://developer.apple.com/library/content/technotes/tn2413/_index.html#//apple_ref/doc/uid/DTS40016228-CH1-TROUBLESHOOTING-WHY_ARE_MY_PRODUCT_IDENTIFIERS_BEING_RETURNED_IN_THE_INVALIDPRODUCTIDENTIFIERS_ARRAY_)
-* [Invalid Product IDs](http://troybrant.net/blog/2010/01/invalid-product-ids/): Checklist of common mistakes
-* [Testing Auto-Renewable Subscriptions on iOS](http://davidbarnard.com/post/164337147440/testing-auto-renewable-subscriptions-on-ios)
 
 I have also written about building SwiftyStoreKit on Medium:
 
 * [How I got 1000 ⭐️ on my GitHub Project](https://medium.com/ios-os-x-development/how-i-got-1000-%EF%B8%8F-on-my-github-project-654d3d394ca6#.1idp27olf)
 * [Maintaining a Growing Open Source Project](https://medium.com/@biz84/maintaining-a-growing-open-source-project-1d385ca84c5#.4cv2g7tdc)
 
+### Troubleshooting 
+
+* [Apple TN 2413 - Why are my product identifiers being returned in the invalidProductIdentifiers array?](https://developer.apple.com/library/content/technotes/tn2413/_index.html#//apple_ref/doc/uid/DTS40016228-CH1-TROUBLESHOOTING-WHY_ARE_MY_PRODUCT_IDENTIFIERS_BEING_RETURNED_IN_THE_INVALIDPRODUCTIDENTIFIERS_ARRAY_)
+* [Invalid Product IDs](http://troybrant.net/blog/2010/01/invalid-product-ids/): Checklist of common mistakes
+* [Testing Auto-Renewable Subscriptions on iOS](http://davidbarnard.com/post/164337147440/testing-auto-renewable-subscriptions-on-ios)
+* [Apple forums - iOS 11 beta sandbox - cannot connect to App Store](https://forums.developer.apple.com/message/261428#261428)
+
 ## Payment flows - implementation Details
 In order to make a purchase, two operations are needed: