The US Supreme Court upheld the ban on the app, just days before President-elect Donald Trump takes office on Monday. The outgoing administration of Joe Biden has put the ball in the court of its successor.

The app started working again on Sunday after Trump said he would sign an executive order to ‘delay the ban’. But why was it banned in the first place?

Here is why TikTok banned in the US

TikTok was banned in the US over national security concerns with a federal law that required its parent company ByteDance to cut ties with the US operations.

The courts, including the Supreme Court, refused to overturn the law, thus effectively banning the app in the country until ByteDance either sells the US operations or shuts it down for good.

“A law banning TikTok has been enacted in the US. Unfortunately, that means you can’t use TikTok for now,” the message to users from TikTok read.

The US lawmakers and officials have sounded the alarm for years about the supposed risks that TikTok’s ties to China pose to national security, and Congress moved last year to force TikTok’s Chinese parent company, ByteDance, to sell its stake in the app or be cut off from the US market. The law gave the company a deadline of January 19.

With no sign of a sale in sight, TikTok’s last-ditch legal challenge failed on Friday when the Supreme Court said the law does not violate the First Amendment.

President-elect Donald Trump has vowed to “save” the app.

Officials in the US have repeatedly warned that TikTok threatens national security because the Chinese government could use it as a vehicle to spy on Americans or covertly influence the public in the country by amplifying or suppressing certain content.

Though the divest-or-ban law passed with bipartisan support, some lawmakers have been critical of the measure, agreeing with TikTok that it infringes on Americans’ free speech rights.

Others have changed their tune as the deadline for a ban neared, including Trump, who tried to ban the app with an executive order during his first term that was struck down in the courts.