In addition to the chatbox showing above the player's head, there should be more options.
Add more options to the chatbox so you can spawn the chatbox in front of you, right on your hands, or also make it grabbable so you can move around the text.
People usually look at your face and not above your head where your username is, so the current placement is not good.
There's also something necessary, to make people notice you, when you send a message you should make a little pop sound, so people are aware about that you just typed something.
Right now it's very easy to type and literally get ignored because no one will notice or see it, think about these features that i just said, please.