Can't call function with ZML Button

Can't call function with ZML Button

Hi,

I have a page where I have a subform and a button made in ZML. My initial goal is simply that onClick, I call a function that updates multiple entries.

Even though the function exist, I am unable to reference it. If I try to reference it manually with a ZML Snippet, it gives me an error message.

How come this particular function is not selectable?