According to the Twitter Support page, Twitter is temporarily turning off the ability to tweet via SMS, or text message, adding that the company will be doing this "because of vulnerabilities that need to be addressed by mobile carriers" and Twitter's reliance on linked phone number for two-factor authentication.
We’re temporarily turning off the ability to Tweet via SMS, or text message, to protect people’s accounts.
— Twitter Support (@TwitterSupport) September 4, 2019
The company also assured that they are working on their longer-term strategy for text message feature.
