“Sorry, TikTok isn’t available right now,” the message read.

Hours before a federal law banning TikTok from the United States took effect on Sunday, the Chinese-owned social media app went dark, and U.S. users could no longer access videos on the platform. Instead, the app greeted them with a message that said “a law banning TikTok has been enacted.”

“We are fortunate that President Trump has indicated that he will work with us on a solution,” the message said. “Please stay tuned!”

In addition, TikTok’s sister app, Lemon8, stopped working and showed U.S. users a message saying that it “isn’t available right now.” Both TikTok and Lemon8 are owned by ByteDance, a Chinese internet giant.

Apple said it removed TikTok and other ByteDance apps, including Lemon8, from its app store, and users said that Google’s U.S. app store also removed TikTok.

TikTok became unavailable after the Supreme Court decision on Friday upholding the law, which calls for ByteDance to sell the app by Sunday or otherwise face a ban. The law was passed overwhelmingly by Congress last year and signed by President Biden. TikTok, which has faced national security concerns for its Chinese ties, had believed it could win its legal challenge to the law, but failed.

The blackout capped a chaotic stretch for TikTok, which had made last-minute pleas to both the Biden administration and President-elect Donald J. Trump for a way out of the law. Until Saturday night, no one — including the U.S. government — was entirely sure what would happen to it when the law took effect. The United States has never blocked an app used by tens of millions of Americans essentially overnight.

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