Replace pages

Hi
I have a 26 page pdf file.
On page 2 I created a field called "one customer start" where the n° 1 appears
On page 26 I created a field called "customer end donation glossary" where the n° 25 appears

Then I created this function to insert into a button on the front page to replace the pages of the file from page 2 to page 26 with a 25-page pdf file called SURNAME DOC CUSTOMER

I created a field called "SURNAME"

Finally I created this function

var s1=this.getField("one customer start").value;
var s2=this.getField("customer end donation glossary").value;
var s4=this.getField("SURNAME").value;
this.replacePages({cPath:"/C/Users/Name Surname/Documents/AUXILIA/practices/"+s4+"/INSURANCE/"+s4+" DOC CUSTOMER.pdf",nStart:s1,nEnd:s2});

This error appears on the console:
TypeError: Invalid argument type.
Doc.replacePages:4:Console undefined:Exec
===> nEnd parameter.
undefined

Please, can someone help me understand where I made the mistake?
Thank you