Sum in Lookup in Monogo C# [closed]

            List<abcd> data = new List<abcd>();            data.Add(new abcd { name = "tbl1", fieldname = "total_amount" });            data.Add(new abcd { name = "tbl2", fieldname = "total_amount_return" });            var Pipeline = new List<BsonDocument>();            var groupFields = new BsonDocument{    { "_id", "$_id" },    { "customer", new BsonDocument("$first", "$customer") },    { "sr_no", new BsonDocument("$first", "$sr_no") },    { "untitled", new BsonDocument("$first", "$untitled") }};            // Perform all lookups first            for (int i = 0; i < data.Count; i++)            {                Pipeline.Add(new BsonDocument("$lookup", new BsonDocument    {        { "from", data[i].name },        { "localField", "_process_id" },        { "foreignField", "_process_id" },        { "as", $"Products{i}" }    }));                // Unwind each lookup result                Pipeline.Add(new BsonDocument("$unwind", new BsonDocument                {                    { "path", $"$Products{i}" },                    { "preserveNullAndEmptyArrays", true }                }));                // Sum each field                groupFields.Add($"{data[i].fieldname}", new BsonDocument("$sum", new BsonDocument("$ifNull", new BsonArray { $"$Products{i}.{data[i].fieldname}", 0 })));            }            // Group by required fields and sum the fields from each lookup            Pipeline.Add(new BsonDocument("$group", groupFields));

This is my Code to Get Sum from 2 or more than 2 Collection. This code is written by chatpgt but there's a problem in it that it it will multiply the total amount and return total with number of row like if total amount is 1,000 and product count in tbl1 is 4 than it will return 4,000 same is it with total amount return.

Any guidance or suggestions would be greatly appreciated.