Roblox complies with COPPA so has to filter out inappropriate text (both toxic language, information regarding contact details, impersonating, dating and many many others).
The filter has different settings based on the age (13- or 13+) and other settings (e.g. chat with friends only, no chat, chat with everyone) of your profile and the profile of whom you are discussing, but the filter is known to be overprotective and block some normal messages.
You can check the Roblox community rules in the help center article Roblox Community Standards.
And if there are certain words / texts that you think should not be filtered then please raise this with Roblox Support.
