"You are not allowed to say that" don't says that you are muted,
You are saying something wrong (Little glitchy sometimes),
say hello and you can say Hello.
If you can't, check your options in-game by the left of the lobby selector, and check if chat is enabled.
If it says the mute reason, you are muted :)
But its says you tried to swear, so say something else like "Hello"