Type mismatch for "get" function

Hello,

I have an issue and I am kinda confused by it. I am trying to write a custom function that calculates the sum of all "Invoiced amount" fields and copies it on the related deal.

When I run the function I encounter a type mismatch error:

Data type of the argument of the function 'get' did not match the required data type of '[BIGINT]'

Here is the script:

taskDetails = zoho.crm.getRelatedRecords("Tasks","Deals",dealId.toLong());

suma = 0.0;

for each task in taskDetails

{

suma = suma + ifnull(taskDetails.get("Invoiced_amount"),"0.0").toDecimal();

}

updateResp = zoho.crm.updateRecord("Deals",input.dealId.toLong(),{" Invoiced_amount":suma});

info updateResp;

The Invoiced_amount fields are currency fields.

Is there any way to solve this? What have I done wrong?

Thank you!