Apple is apparently issuing automatic refunds for those who purchased the Peace ad blocker for iOS 9 before it was pulled from the App Store by developer Marco Arment shortly after its debut. On his blog, Arment notes that more than Apple's decision to perform automatic refunds is exceedingly rare:

As far as I know, this effectively never happens. When I decided to pull the app, I asked some Apple friends if this was even possible, and we all thought the same thing: iTunes billing works the way it works, period, and no special cases can be made.

However, Apple has contacted Arment to let him know it has initiated proactive refunds for all who bought the app. Prior to this, Arment notes, more than 13,000 users had received refunds through the manual request process. If you happen to have purchased the app, you should expect a notification of the refund from Apple within the next couple of days.