How to make firebase rule to prevent write by property size?

I have chat rooms with messages structure like this:

messages                          // collection
messages/docId                    // docId is Id of the room
messages/docId/roomMessages       // collection
messages/docId/roomMessages/docId // actual message

message example:
{
  fromUid: "",
  messageText: "",
  sentAt: date
}

match /messages/{docId} {
      allow read: if isloggedIn(request);
      allow create: if isloggedIn(request);
      
      match /roomMessages/{docId} {
        allow read: if isloggedIn(request);
        allow create: if canCreateMessage(request);
        allow write: if canCreateMessage(request);
      }
    }

function canCreateMessage(request) {
      let isSignedIn = request.auth.uid != null;
      let isOwner = request.auth.uid == request.resource.data.fromUid;
      let isNotTooLong = request.resource.data.messageText.size() < 5;
      return isSignedIn && isOwner && isNotTooLong;
}

but I still can save message that is longer than 5 characters. But not idea why?
Code that write message

const messageRef = firestore()
  .collection('messages')
  .doc(roomId)
  .collection('roomMessages')
  .doc();

await firestore().runTransaction(async transaction => {
  transaction.set(messageRef, {
    fromUid: authenticatedUser.uid,
    messageText: message,
    sentAt: firestore.FieldValue.serverTimestamp(),
  });
})

First part to show where I put rules maybe previous rules mess up:

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
  
    match /{document=**} {
      allow read; 
      allow write: if isloggedIn(request);
      allow create: if isloggedIn(request);
      allow update: if isloggedIn(request);
      allow delete: if isloggedIn(request);
    }
    
    match /messages/{docId} {
        allow read: if isloggedIn(request);
      allow create: if isloggedIn(request);
      
      match /roomMessages/{docId} {
        allow read: if isloggedIn(request);
        allow create: if canCreateMessage(request);
        allow write: if canCreateMessage(request);
      }
    }