This story is available exclusively to Insider subscribers. Become an Insider and start reading now. A leaked Facebook memo to advertisers lays out how Apple's new iOS 14.5 will impact ad campaigns. The memo warns that results will fluctuate and audiences will shrink. Certain attribution tools will no longer be available. Facebook sent a memo to advertisers April 28 detailing the effects Apple's new privacy settings will have on ad campaigns. The memo, obtained by Insider, elaborates on an April 26 blog post advising advertisers on how to prepare for the change. Facebook warned that the results of their ad campaigns will fluctuate, with the size of audiences shrinking as users gradually update their Apple devices in the coming weeks. Facebook and Instagram will automatically opt those users out of tracking settings.