How to filter messages on my backend

I am working on global matchmaking and wondering how to filter messages on my backend
(I am using HttpService and not memoryservice)

What do the messages and filtering process look like?

basically, there is global chat and I filter messages before they are sent but an exploiter can bypass that

they should already be filtered just send the filtered message over HTTP POST

(Assuming you have a custom chat and are using TextService:FilterStringAsync())

Yea thats what I do, but an exploiter can bypass it

Well not easily if you filter the message on the server. By the way, nothing is 100% secure.