Are you using Facebook mobile Web app for chatting, if yes, Facebook has announced that they will be removing the messaging functionality from Facebook mobile Web app soon. Users will need separate Messenger app soon for using the chat functionality, which leads Facebook Web app with bare-bone options for those users who were ignoring the standalone Messenger app.
In case you are wondering, those who are using Facebook mobile Web app will get the following notice constantly:
Although Facebook has not disabled the messaging option from its Web based platform, but soon the Messenger will be the only way to communicate with your friends on Facebook. The clear reason behind this move is to promote its Messenger app which hit 900 million milestone in April, and Facebook obviously wants you to use its Messenger app and lead them to their new milestone of 1 billion users as soon as possible.