Why it is not supported the Update credit notes in Zoho Books with custom function?

Why it is not supported the Update credit notes in Zoho Books with custom function?

i Need update data of the credit Notes with a custom funcion, but when i Execute the function, i reciver a error:

Invalid value for parameter - module. The allowed values are: contacts, invoices, customerpayments, items, estimates, recurringinvoices, expenses, purchaseorders, salesorders, journals, projects, bills.

And when i reed the document of Deluge Task ( updateRecord), I find that the module Credit Notes is not supported, but it is supported in other task.

And my Question is...  WHY?