Custom function not firing

Custom function not firing

Hi, 
I'm experimenting with Zoho CRM.
I'v tried to create a Workflow that triggers a field update and a custom function.
I can see the field update but not the custom function triggered.
The CF simply creates an Account with the name of the potential updated (I know this has no sense but it's just a test).
See attachment for the Custom Function body.
I can't see any error nor a reason for this CF not triggered.
Thank you 
Enrico