why file path dosnt apear when i run google app script code

This is my gs code:

function onOpen(){
  var ui = SpreadsheetApp.getUi();
  var menu = ui.createMenu("bot")
  menu.addItem("test", "runForm")
  menu.addToUi();
}
    
function runForm() {
  var html = HtmlService.createHtmlOutputFromFile('picbox')
  SpreadsheetApp.getUi().showModelessDialog(html, 'form');
}
    
 function f(filePath) {
    SpreadsheetApp.getActiveSheet().getRange("A15").setValue(filePath)
    return true;
 }

and this is my html code:
picbox.html:

<!DOCTYPE html>
<html>
  <head>
  </head>
  <body> 
    <input type="file" id="file123" />
    <input type="button" value="send file path"  onClick="func();"/>   
    <script>
      function func() {
        var a = document.getElementById("file123").Value
        google.script.run
        .withSuccessHandler(function(){google.script.host.close();})
        .f(a);
      }
    </script>
    </body>
</html>

when i run it the form apear but the file path dosnt shown on A15 cell. i know that f function calld and working i jusr dont know why the file path dont written.