How to create custom function?

How to create custom function?

Hi,

This is probably a basic question :)
I would like to create Custom Functions in Zoho CRM. I tried to follow this tutorial:  https://www.zoho.eu/crm/help/automation/custom-functions-programming.html, but I guess this is outdated. In my Automation menu (in Settings of Zoho CRM), I only have "Workflow Rules", "Actions" and "Scoring Rules". And I cannot find the Custom Function option anywhere.

I even upgraded from Basic to the Professional edition to see if I could get these options but without any success. Do I need entreprise?

Could you please help?