(Bloomberg)—Facebook Inc.’s system for buying ads is acting up just days before one of the busiest online shopping days of the year.

The technology, which companies and agencies use to buy Facebook ads, was down for some major users earlier in the day on Tuesday, according to a media buyer and another person familiar with the situation. The system is now back up but working slower than normal, the people said.

“Campaigns that are live and running should not be affected and are still being delivered. However, advertisers may experience issues creating new campaigns and making changes to existing campaigns,” a spokesman for Facebook said in email.

The hiccups hit just before Black Friday, one of the biggest U.S. shopping days of the year. Advertisers are currently flooding social media, email inboxes and websites to get people excited about their products ahead of the holiday gift-buying period.