The error occurred when users clicked on video carousels to view video ads placed by advertisers. Facebook said affected advertisers will receive a full credit for charges incurred because of the error.
The company said it had fixed the bug, which was not found on the desktop version or the mobile app.
Facebook goes on to highlight how the miscalculation only affected media buyers that had used its video ad carousel unit or had bid on link click.
Since September a year ago Facebook has on five different occasions acknowledged that the company has either understated or overstated the metrics that publishers and advertisers utilize to determine how effective their ads or content is on a digital platform.
The scale of the bug was relatively minor, as the average refund payment to affected advertisers was only around $10, Marketing Land reported.
Facebookreports that the impact from a billing perspective was 0.04 per cent of ad impressions, due to mobile web making up a small percentage of overall ad impressions on Facebook in general.
Carolyn Everson, Facebook, vice president, global marketing solutions, added: "We are committed to transparency with our partners when it comes to driving results on Facebook".
Facebook wants to show advertisers that it is making good on its promise to ramp-up transparency levels with its ad offering, by holding its hands up plus offering to make amends, whenever its product suite has misfired.
As the image above indicates, the bug was limited to a certain set of conditions, whereby advertisers were incorrectly billed when users clicked on the videos to enlarge them.
The company said, "Regardless of how many impressions were affected, we take all bugs seriously and apologize for any inconvenience this has caused".
The newly discovered bug is the latest in a series of embarrassing errors for Facebook.
"While advertisers don't like to see this kind of thing, they feel if there was value in the platform before the issue came up, there will still be value despite this problem", he says.