Update Matched Object In Array

Question

I am trying to update nested values in a MongoDB document but I get the following error : "cannot use the part (Accounts of Accounts.Rules.Frequency) to traverse the element"

Below is the structure of my document and the code I am trying to run :

{"_id" : ObjectId("5ab2313bf7951607c1072e54"),
 "Customer_id" : 2,
 "Accounts" : 
  [ {"Account_id" : NumberLong(1398868310133024),
    "AccountType" : "admin",
    "Created_at" : "01-01-2018",
    "Rules" : {"Goal" : 200,
               "DoNotDisturbFrom" : "22",
               "DoNotDisturbTo" : "8",
               "Frequency" : "weekly"}
    }, 
   {"Account_id" : 2,
    "AccountType" : "user",
    "Created_at" : "01-02-2018",
    "Rules" : {"Goal" : 200,
               "DoNotDisturbFrom" : "20",
               "DoNotDisturbTo" : "12",
               "Frequency" : "monthly"}
    }
 ]
}

Here is the code :

result = collection.update_one({"Accounts.Account_id":1398868310133024}, {'$set':{"Accounts.Rules.Frequency":"monthly"}})
print result