I am trying to write a app script that add some custom properties to the file that stored in shared Drive. After trying multiple ways and reading through the documentationtext, I still can’t succeed adding or getting properties of a file.
Here is my coding for adding the AppProperties:

function addAppProperty(fileId) {
  try {
    let file = {
      'appProperties': {
        'department': 'Sales'
      }
    };
    // Updates a file to add an app property.
    file = Drive.Files.update(file, fileId, null, {'fields': 'id,appProperties'});
    console.log(
        'ID: %s, appProperties: %s',
        file.id,
        JSON.stringify(file.appProperties, null, 2));
  } catch (err) {
    // TODO (developer) - Handle exception
    console.log('Failed with error %s', err.message);
  }
}

which is from the documentation, this works well, but when I try to return the properties of a file and search for property, I’ve encountered many errors:

function getProperty() {
  var files = DriveApp.searchFiles('properties has { key="department" and value="Sales" }');
  
  if(files.hasNext) {
    var file = files.next();
    console.log(file.getName());
  }
  else{
    console.log("No file founded")
  }
} 

With error Exception: Invalid argument: q, regard to this line var file = files.next();

I have no clue how to solve this problem, Very appreciate to any kind of Help!