Firebase Database rule for unknown child nodes - flutter

Question

I'm creating a chat app where data are stored like the image given below.
I want to add a validation rule for "Text" to be less than 300 characters long. I used the validation rule:
"TextChannels":{
"Anime_Weebs":{
".validate": "newData.child('Text').val().length < 200"
},
But this rule is not working. Instead any type of text is getting rejected.
This is my database:
And this is my Flutter AddMessage code:
_addMessage() {
final user = FirebaseAuth.instance.currentUser;
final time = DateTime.now().toUtc().millisecondsSinceEpoch;
_dbRef
.ref('TextChannels/${channelName}/Messages/')
.child('${time.toString()}${user!.uid}')
.set({
'Author': user.displayName,
'Author_ID': user.uid,
'Author_Username': username,
'Time': time,
'Text': _message,
'Delivered': false,
'Day': days
});
}

Answer 1

This rule that you have:
"TextChannels":{
"Anime_Weebs":{
".validate": "newData.child('Text').val().length < 200"
},
This rule says that your database has a path TextChannels/Anime_Weebs that has a child node Text whose length you want to restrict. But if we look at your database, there is no path TextChannels/Anime_Weebs/Text - and since a non-existing value is definitely not longer than 200 characters, the rule doesn't block any write operation.
If you want to apply a rule to all child nodes under a path, you need to use a wildcard variable to capture the unknown part of the path:
"TextChannels":{
"Anime_Weebs":{
"Messages": {
"$messageId": {
".validate": "newData.child('Text').val().length < 200"
}
}
},
So here the Messages and $messageId rules are new compared to your rules, and the latter indicates the the .validate rule should be applied to each child node of TextChannels/Anime_Weebs/Messages.