Chat message could not be sent?

Whenever I press t to open the chat, it says "Chat message could not be sent" in red and only visible to me in the chat. This happens on every Minecraft server (yes also on private ones) and I've already tried to log in again

I look forward to an answer

Your chat is set up so that you can only send / receive commands. To change it, press ESC> Options…> Chat Settings… And click on Chat: Show commands only and then again on Chat: Hidden.

Chat is set for everything