I have composed a list of some bugs and suggestions that I recommend you take onboard.
Suggestions:
You should add UIS (UserInputService) as a way for players to send message. For example, if I click “/” on my keyboard, it highlights the chat window so I can straight away begin typing. Same with the “enter” key, I would much rather click the “Enter” key than move my mouse over to click the tick/send button
Another suggestion is lowering the cooldown, if you make a typo or typing error and want to immediately correct it, the cooldown prevents you. I would recommend creating a threshold system where you can only send 5’ish messages in quick succession before cooldown kicks in. If you don’t know how to do this, I’d be happy to help you.
Bugs
I did not find many bugs in the system which is great, it shows that you have made it well. I did however, find at least one. If you spam the send button with either an empty message or a message with text multiple times with an autoclicker or by manually clicking very quickly, it breaks the chatbox. Essentially, if you spam the send button and then try and type a message you get the cooldown error which last for a very long time, not sure how long but certainly longer than 5 minutes.
Note: I found this line funny if Player.Name == "RenderedPhysics" or Player.UserId == 3674967405 then
Chat filtering is enabled in every game, and everybody knows that.
I think this should just say Click here or press '/' to chat like the original one. The rest of the UI looks acceptable though!
There shouldn’t be any backdoors in this module. If this is just to give the module owner a badge, it shouldn’t be hardcoded like this. It shoud be exposed in a module which the game creator can change.