.findIndex()

The Problem

.findIndex() is breaking. I'm providing it with a string, but it's saying "It's not a function"

Objective / Context

Auto reply to property inquiry

Function does the following:

• Scans the inbox to identify inquiry.

• Breaks down the email, storing the data in variables.

• Scans a spreadsheet with information about all of our homes for sale. Matches the property ID in the email against the spreadsheet looking for the match.

• Replys to the email with data stored in the spreadsheet that matches that property.

Where I am up to

I am able to identify the email. I'm then able to scan through the email and pull the relevant information.

The Code

function autoReply() {
var queryInbox = "is:unread from:(example@gmail.com) to:(example@gmail.com) Example Text:"; // Email Identification
var locatedEmail = GmailApp.search(queryInbox); // Search Inbox for Identification
locatedEmail.forEach(thread => {
  var messages = thread.getMessages();
  if (messages.length === 1) {
    // BREAKING DOWN THE EMAIL
    var msgBody = messages[0].getPlainBody();
    var identityNumber = msgBody.split("\n")[1].replace('Property ID: ','');
  
    // SPREADSHEET      
    var SS = SpreadsheetApp.openById('exampleId').getSheetByName("Sheet1");
    var column = 1; // column Index
    var columnValues = SS.getRange(2, column, SS.getLastRow()).getValues(); //1st is header row
    var searchResult = columnValues.findIndex(identityNumber); //Row Index - 2
    var rowID = searchResult + 2;
  
    var houseAddress = SS.getRange(rowID, 2).getValue();
  
    // EMAIL BODY
    var body = "<p>Hi, thank you for emailing us about " + houseAddress + ".</p>";
    var options = { name: "Property Enquiry", htmlBody: body };
    thread.reply(body, options);
    thread.markRead();
    thread.moveToArchive();
  }
});
}

Example Email

Example Spreadsheet

Additional Information: Error is showing that it is passing a propertyID as a string to the .findIndex