Update subscriptions.md

Added note about not having the most recent version

get-help/subscriptions.md

@@ -81,6 +81,7 @@ If you find that you are unable to purchase a Pro subscription whilst following
 
 - Parental permissions are enabled which are preventing in-app purchases
 - There is a problem with your network connection
+- You do not have the most recent version of Infinite Flight installed
 - You do not have an official version of the app
 
 
@@ -171,4 +172,4 @@ Step 5
 
 Tip
 
-: Make sure that if you are already logged in to the Infinite Flight Community on the device, it is the account that you would like to link as it will automatically register this
+: Make sure that if you are already logged in to the Infinite Flight Community on the device, it is the account that you would like to link as it will automatically register this