Facebook said on Wednesday it was underestimating the results of its advertising activity on Apple iOS devices, acknowledging that recent privacy changes made by the iPhone maker have made it more expensive and difficult for brands to advertise on Facebook. Shares of the social media giant were down 3.7% to $ 344.32 in morning trading.

Facebook said in a blog post that it estimates it underestimates “conversions” by 15%, an industry term that includes buying products or other actions that a person takes after seeing an advertisement, adding that the figure varied among individual advertisers.

Facebook said it believes actual conversions such as app sales and downloads are higher than reported.

The announcement comes as Facebook and the digital advertising industry as a whole continue to grapple with the privacy controls Apple implemented in April, which are designed to prevent digital advertisers from tracking iPhone users. for advertising purposes without their consent.

Facebook has hit back at the changes, arguing it would hurt small businesses that rely on targeted advertising to find new customers.

The social media company previously warned investors that there would be a “bigger impact” of Apple’s changes on Facebook’s advertising business in the third quarter compared to its second quarter.

In Wednesday’s blog post, Facebook outlined the steps advertisers should take to better measure the results of their ads. The company said it is investing in new tools and capabilities to help brands with their marketing amid Apple’s changes.