[{"total_price":8.92,"paymentStatus":"Paid","refundedAmount":5},{"total_price":20.92,"paymentStatus":"Paid","refundedAmount":15}]

db.collection.aggregate([{"$project":{total_price:1,paymentStatus:1,refundedAmount:1,description:{$concat:["Refunded ",{$toString:"$refundedAmount"}]}}}])