Reason: Unable to resolve reference of payload..

%dw 2.0
 
import * from dw::core::Strings
 
var regExDateTime = /\d{4}-[01]\d-[0-3]\dT[0-2]\d:[0-5]\d:[0-5]\d\.\d+([+-][0-2]\d:[0-5]\d|Z)/
var regExDate = /^\d{4}\-(0[1-9]|1[012])\-(0[1-9]|[12][0-9]|3[01])$/
var regExBoolean = /^(true|false)$/
var id= payload.ChangeEventHeader.recordIds[0]
 
output text/plain
---
id

My DW is somewhat big having some calculation for sake of simplicity I just pasted 4 lines of code only.

In that 4 line itself I am getting below error

Scripting language error on expression '%dw 2.0
 
import * from dw::core::Strings
 
var regExDateTime = /\d{4}-[01]\d-[...'. Reason: Unable to resolve reference of payload..

I even tried by defining meta data for payload as like below

var id= payload.ChangeEventHeader.recordIds[0] as String 

var id= payload.ChangeEventHeader.recordIds[0] as String  default 'axd123'

But nothing helps