TIkTok's 170 million users started receiving a "services temporarily unavailable" notice late Saturday night and the app was no longer available in Google and Apple's app stores as a law to ban the app was set to take official effect at midnight.

Why it matters: It's the first time the U.S. has banned a major online platform of this scale.

Between the lines: In declining to enforce the ban during his last day in office, President Biden essentially shifted the responsibility for enforcing the law to incoming President Trump.

• Trump has indicated that he will try to keep TikTok alive in the U.S., but facing hefty fines, Google and Apple likely chose not to take the risk of violating the law.

What they're saying: Apple has not commented on their plans. Google declined to comment.

Catch up quick: For app store operators and cloud-services vendors like Oracle, which runs the backend for TikTok in the U.S., the ban story has proven complicated.

• Although the Supreme Court upheld the ban Friday, lawmakers have been split on whether they should try to find a way to extend the ban's deadline or keep TikTok shut out of the U.S. unless it found a U.S. buyer.

What to watch: Trump could decide to extend the deadline by 90 days, but he would have to show that legally binding negotiations for a sale of TikTok to U.S. owners are underway.

• There are U.S. players who are interested in buying TikTok, but any deal to acquire the app would also face the hurdle of winning China's approval.
• Trump could also issue an executive order or ask his attorney general not to enforce the law.