It seems that Twitter is trying to tackle its recurring spam problem by disabling links in direct messages. Yesterday users reported that they could only send links if they came from Facebook, Instagram and Twitter itself. Anything else would bring up a pop-up message reading, “Failed to send message. Whoops! You already said that.”
This could also be a response to Twitter’s latest feature, which allows a broader range of accounts to send direct messages between each other. This would theoretically make it easier for malicious parties to send malware to Twitter accounts – hence the sudden problem with external links.
At the time of writing Twitter hadn’t commented on the issue, but various sources are reporting that there is a “technical issue”.