passing process variable to interface(Records Tutorial)

Hi,

     I am using 18.1 and trying records tutorial by following https://docs.appian.com/suite/help/18.1/Records_Tutorial.html

     I was stuck at Add a Related Action point 4 where we need to pass process variable to query rule. I know its not in very detailed but generic steps . As a newbie, I  need guidance in proceeding further in the tutorial.

step 4: For the User Input activity, assign the task to "=pp!initiator", and create a form titled "Update Phone Number" with one text field called "New Phone Number" that has a default value of rule!getEmployeeById(pv!employeeId).phoneNumberand saves into ac!newPhoneNumber. ac!newPhoneNumber should then be saved into a process variable so that it can be accessed by other nodes later in the process.

           Here text field for new Phone Number that i am creating.

a!textField(
  label: "New Phone Number",
  labelPosition: "ABOVE",
  value:  rule!getEmployeeById(pv!employeeId).phoneNumber,
  saveInto: {ac!newPhoneNumber},
  refreshAfter: "UNFOCUS",
  validations: {}
)

The error i am getting in interface is "Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error: Invalid variable(s) found: pv!employeeId,ac!newPhoneNumber."

      I would like to know how do i create activity class variable ac!newPhoneNumber and pass it to another process variable?  Any help would be appreciated.

     Attaching screen shots for process variable declaration and  query rule that i created

Thanks.