I received an unexpected advertising credit.
There are a variety of reasons why Facebook may issue an advertising credit. Such credits will be automatically added to your ad account's payment methods, and when you run ads, the charges will first be deducted from the credit before your credit card is charged.
If our system detects that there have been invalid clicks on your account, we may automatically credit your account with the value of those clicks. Please note that we filter out some clicks for a variety of reasons before they ever appear in your reports or charges. We may issue a credit if we identify certain clicks as invalid after you've been charged for them.
Similarly, if there are any issues on our end that interfere with the correct delivery of your ads, Facebook may issue a credit equal to the value of any incorrectly delivered clicks.
