[{"key":1,"someValue":"abc","installments":[{"number":1,"payments":[{"paymentNumber":1,"value":29},{"paymentNumber":2,"value":22}]}]},{"key":2,"someValue":"xyz","installments":[{"number":1,"payments":[{"paymentNumber":3,"value":10},{"paymentNumber":4,"value":1},{"paymentNumber":5,"value":5}]}]}]

db.collection.update({"installments.payments.paymentNumber":4},{"$push":{"installments.payments":[{"receipts":[{"receiptNumber":1}]}]}})