I'm not aware that a new player can't chat on the in-game chat. I more suspect it was just an issue with how to get it sent, which could be device/browser dependent. Usually if you type something, you can just hit Enter if you don't leave the chat box. If you click outside it, I think then you must click on that little do-hickey at the right of where you're typing to get it to go. (Or you may need to do that anyway.) And you may need to click inside the typing box again before doing that. (Sorry I'm vague, but I've been using it for so long that I sort of do things by habit and don't always know what exactly I'm doing.
)
But you don't have to "activate" it as a new player, no. And not allowing you to use it as a new player seems counter-productive, since appearing stuck-up to other players might make them not like you, so that makes no sense. (I'm not sure you're allowed to use the main chat when you're new, but that's different.)