Twitter is having a rough start to the week. On Monday, the social network experienced several issues, including outbound links in tweets not working and images not loading in timelines. 

Instead of going to the intended sites, links in tweets served up an error message that read: “Your current API plan does not include access to this endpoint, please see https://developer.twitter.com/en/docs/twitter-api for more information.” 

Twitter acknowledged the problems, saying in a tweet on Monday that “some parts of Twitter may not be working as expected right now” due to an “internal change that had some unintended consequences.” As 10:05 a.m. PT, Twitter appeared to have fixed the issues and said things “should now be working as normal.”

Elon Musk, the tech billionaire who bought Twitter in October, followed up on the issues, saying in a tweet that a “small API change had massive ramifications.” He added that Twitter’s “code stack is extremely brittle for no good reason. Will ultimately need a complete rewrite.”

Twitter in February said it would start charging for access to a “basic tier” of the social network’s API, or application programming interface, which developers and researchers use to analyze public tweets. The change was originally set to take place on Feb. 13 but was delayed, with the social network saying the rollout would happen “over the next few weeks.”

Plans to put Twitter’s API behind a paywall are among a number of changes announced at the social network since Musk took over the company. Last month, Twitter rolled out the ability for Twitter Blue subscribers to tweet 4,000 characters, up from the typical 280 characters. 

Twitter didn’t respond to a request for additional information.