Chats aren't being added to the ArrayList even though I can see that they are being saved to Firebase

Was hoping that someone could help me out with the logic for this code. I am trying to implement a chat, and the way that I have it set up it seems like it should work and flow well (if not, someone tell me how to make it better), but anyways, I can see that the chats are being added and saved to Firebase just fine, but the problem is they don't get added to the ArrayList for some reason so that the user can see the chat that they have sent or received from someone else.

Can someone tell me which part of my code I have wrong so that I can fix it?

That's not a bad flow the way I have it set up, is it?

MessagesActivity Here I add the chats to Firebase

 final DatabaseReference chatReference = FirebaseDatabase.getInstance().getReference("Chat List").child("Sender").child(mFirebaseUser.getUid()).child("Receiver").child(mId);
        chatReference.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                if (!dataSnapshot.exists()) {
                    chatReference.child("Receiver").setValue(mId);
                    chatReference.child("Timestamp").setValue(ServerValue.TIMESTAMP);
                    chatReference.child("Sender").setValue(mFirebaseUser.getUid());
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

        final DatabaseReference chatReferenceReceiver = FirebaseDatabase.getInstance().getReference("Chat List").child("Receiver").child(mId).child("Sender").child(mFirebaseUser.getUid());
        chatReferenceReceiver.child("Receiver").setValue(mId);
        chatReferenceReceiver.child("Timestamp").setValue(ServerValue.TIMESTAMP);
        chatReferenceReceiver.child("Sender").setValue(mFirebaseUser.getUid());

ChatFragment Here the chats should be added to the ArrayList

 DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Chat List").child("Sender").child(mFirebaseUser.getUid()).child("Receiver");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                mChatList.clear();
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                    Chatlist chatlist = snapshot.getValue(Chatlist.class);
                    mChatList.add(chatlist);
                }

                if (mChatList.size() == 0) {
                    mNoMessages.setVisibility(View.VISIBLE);
                } else {
                    mNoMessages.setVisibility(View.GONE);
                    chatList();
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

So Google is your friend here. Others have struggled with this in the past and there are articles/posts on eg. Medium, SO that give ideas. The one I liked and used - no shame in copying the good work of others is in this Medium post: https://medium.com/@ngengesenior/database-structure-of-one-to-one-chat-app-with-firebase-93f813184dfe

It covers both Firestore and RTDB. Basically, for RTDB your list of chats is managed using a concatenated (compound) key of both userids, the two userids being sorted alphabetically before creating the key eg. userid1 = xxxx, userid2 = bbbb, compound key is bbbbxxxx (FB userids are 28 chars long so the compound key is 56 chars).
In this way, with one database read to the compound key you get all the chat messages between those two users, no matter which one was the sender or receiver. You keep a bool indicator on the message to say if the first userid in the compound key was the sender and with that information you can parse the compound key to determine the userid of the sender and receiver - that was my improvement over what is described in the article, he still stored the sender and receiver ids as properties. Cuts out a huge amount of data duplication and should simplify the code needed to handle chats. I don't use Java so can't help you with the code.