我已经接管了一个项目，其中有以下数据模型在firestore：
/聊天/{聊天ID}/消息/{消息ID}

/Chat/{chatId}
{
  users: ["24","51"]
  messages: [ //collection
    {message:"...", sender: 24, time:"...", users: ["24","51"]},
  ]
}

通过flutter我读聊天通过：

StreamBuilder<QuerySnapshot>(
  stream: FirebaseFirestore.instance
             .collection("Chat")
             .doc(chatID.toString())
             .collection("messages")
             .orderBy("time", descending: false)
             .snapshots(),

我需要确保只有参与聊天的两个用户才能阅读消息，但我很难做到这一点。
我当前的规则如下所示：

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {  
    match /Chat/{chatId}{
      allow read: if "24" in resource.data.users //24 is being replaced with request.auth.uid when it works
      allow write
      
      match /messages/{messageId}{
        allow read: if "24" in resource.data.users //24 is being replaced with request.auth.uid when it works
        allow write
        }
    }
  }
}

与上述，我得到一个权限错误时，试图通过flutter列出聊天，它给出了错误：

Chat/1103/messages failed: Missing or insufficient permissions.

如何编写一个规则，使只有两个用户能够读写邮件？