Permission Denied when rules updates with user authentication

Question

This is my real rime database.

This is the code i used to create db.

 const db = firebase.database()
 const frRef = db.ref('Foreign/' + UserId);

frRef.set({
     });
   });

` this is the rules i applied here.

         "foreign": {
  ".indexOn": ["UserId"],
  "$UserId": {
    ".read": "auth.UserId == $UserId",
    ".write": "auth.UserId == $UserId"
  } },

But i got the error "permission denied." any wrong with the implementation. i want only the users with these userids like 99663384, needs to read and write data only . any help would be appreciated. Thank you.