Show or hide a page based on a form field when the pdf is generated by API

I've tried to put in the related field inside the properties> validate>Run custom validation

var t1 = getTemplate("Page 5");

var t2 = getTemplate("Page 4");

// Add page 5 when is less than 0 other case, add page 4

if (GROSS_PREMIUM < 0) {

t1.spawn({nPage: numPages, bRename: true, bOverlay: false});

} else {

t2.spawn({nPage: numPages, bRename: true, bOverlay: false});

}

But it ignore my javascript code, also I tried, just to try, to put this inside the first condition: 

this.deletePages(4);

But continue doing nothing.

The other place where I put the code was in

In Will save Wil print, because the action need to be executed automatically. 

But nothing.

I'm creating the documents using Oracle BI Publisher to link Adobe templates (using the form fields) with a data model and get the data from database. Later built a service to get the url for all the documents that are in the repository of BIP for this specific data, and finally download the url that contains the document PDF.