I have tried to purchase the app on both my ipad, and mac, and in both cases i am unable to purchase and install the app from the app store.  I get the message

"Purchase of this item is not currently available.

This item is being modified.  Please try again later."

This has been occurring all day and I'm unsure what the cause is.  I have read that at times this message can happen for about 3 hours when a price change is occurring however i have been seeing this all day.