Firebase - add database rules - Path contains invalid characters

Actually, this Firebase DB error is frequently caused by an outdated webpage cache. All you need to do is refresh the Realtime Database webpage, and then you'll be able to add your new values:

You are adding rules at wrong place. That is the reason for downvotes. This is the data structure not your rules document.

Put json rules under database rules tab. You have to put rules here. Please check.