Zoho Invoice - Need Deluge Coding Help

Hello,

I would like to write a code for calculating sales commissions after creation of each invoice.

I added a custom field for commission percent to CRM Contacts module and synced this module to Zoho Invoice.

Custom field for commission percent : cf_commission_percent

Custom field for commission amount : cf_sales_commission

Formula : Sales Commission = Invoice Total*cf_commission_percent/100

My code is as follows but it is not working. Any help is appreciated.

customerID = invoice.get("customer_id");

subtotal= invoice.get("sub_total");

sales_commission= invoice.get("cf_sales_commission");

contactMap = List();

contactMap = zoho.invoice.getRecordById("Contacts",717534537,customerID);

contact = contactMap.get("contact");

commission_percent = contact.get("cf_commission_percent");

sales_commission = floor(subtotal * commission_percent/100);

updateparams = zoho.invoice.update("invoice", 717534537, sales_commission);

info updateparams;