[{"_id":"61f15af01a3c53dfa87e38ed","user":"61f15af01a3c53dfa87e38e6","transactions":[{"amount":50,"category":"Bills","type":"Expense","_id":"61f15af01a3c53dfa87e38ee"},{"amount":100,"category":"Lottery","type":"Income","_id":"61f15af01a3c53dfa87e38ef"},{"amount":200,"category":"Salary","type":"Income","_id":"61f15af01a3c53dfa87e38f0"},]}]

db.collection.update({user:"61f15af01a3c53dfa87e38e6"},{$pull:{"transactions":{_id:"61f15af01a3c53dfa87e38f0"}}})