electron "TypeError [ERR_INVALID_ARG_VALUE] The argument 'args' is invalid"

I'm creating an electron application that would launch another application. When try to, i get the TypeError [ERR_INVALID_ARG_VALUE] The argument 'args' is invalid error.

This is my code in the renderer:

const { ipcMain } = require('electron')

var authType;

var username = "username";
var password = "password";

$(".buttonJSMain").click(function() {
    authType = 'authType';
    var str = authType + " " + username + " " + password;
    ipcRenderer.send('run', authType + " " + username + " " + password);
})

This is my code in the main thread:

ipcMain.on('run', (event, customarg) => {
  var child = require('child_process').execFile;
  var executablePath = path.join(__dirname, "/loader/application.exe");

  child(executablePath, customarg, function(err, data) {
      if(err){
        console.error(err);
        return;
      }
  
      console.log(data.toString());
  });
})

When I run it, I get this error: TypeError [ERR_INVALID_ARG_VALUE]: The argument 'args' is invalid. Received 'authType username password'