Error with If formula

Error with If formula

I've got this super simple If formula, what is the reason for the error?

If ( LEN(${Leads.Trial Slot Option}) == 3,'y','n')

Syntax Error. Check the examples for any functions you're using to see if you formatted them correctly. Make sure your fields are formatted like this: ${Module Name.Field Name}.

The field ${Leads.Trial Slot Option} is a pick list field.

I tried these too and same error:
If ( LEN("asdasd") == 3,'y','n')
If ( LEN('asdasd') == 3,'y','n')