There was a little glitch on Facebook – and now the social media giant has to refund advertisers for that.

Looks like Facebook found and fixed a bug that misattributed some clicks on video carousel ads as link clicks. According to Facebook, the bug only affected mobile web browsers, not desktop or the mobile app.

This affected the video carousel ad unit; when the advertiser chose to bid on link clicks; and for people who were on smartphone web browsers. This means that advertisers are being billed for link clicks when it was just users enlarging and watching videos. Facebook will refund advertisers with full credit for the charges they incurred for these misattributed clicks.

According to Facebook, most users use Facebook through the app on their phones, and mobile web browser ad impressions make up a small percentage of the overall ads impressions people see on Facebook.

“Given that this bug related to mobile web for smartphones only, and specifically for video carousel ads that bid on link clicks, the impact from a billing perspective was 0.04% of ads impressions. Regardless of how many impressions were affected, we take all bugs seriously and apologize for any inconvenience this has caused.” Facebook wrote.