As Elon Musk's social network began letting paying users to post tweets longer than 4,000 characters on Wednesday, tens of thousands of Twitter users reported issues.
"Twitter may not be working as expected for some of you," the company tweeted.
"We are aware of the issue and are working on getting it fixed."
Early afternoon in Silicon Valley, Twitter troubles spiked at the website Downdetector and continued for about two hours.
Online users have complained about being unable to post messages, having exceeded a daily tweet limit, and being unable to send direct messages.
According to US media reports, Twitter put a daily limit of 2,400 tweets on its operations to reduce strain.
Additionally, TweetDeck, a popular dashboard for managing and viewing Twitter accounts, had stopped working.
On the same day, Twitter added a length perk to its Blue subscription service, which costs $8 per month.
According to Twitter, subscribers can now post tweets of up to 4,000 characters, far greater than the 280-character limit for non-paying users.
"Don't worry, Twitter is still Twitter," the tech company wrote in a lengthy tweet.
"Longer tweets can cause a lot of scrolling, so they'll be limited to 280 characters and you'll notice a 'Show more' prompt to read the full Tweet."
Twitter's workforce was slashed after Musk became the owner of the San Francisco-based company last year, raising concerns about the company's ability to maintain operations.
The US tech media reported Wednesday that Musk told Twitter staff to focus on troubleshooting rather than new features.
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