Firestore Cloud Functions in iOS - Delete collections DEADLINE EXCEEDED

I want to delete a collection containing subcollections. I'm trying this method from the Firestore Documentation.

I have installed Firebase CLI and added the following function to the index.js :

exports.recursiveDelete = functions
  .runWith({
    timeoutSeconds: 540,
    memory: '2GB'
  })
  .https.onCall((data, context) => {
    const path = data.path;

    console.log(
      `User ${context.auth.uid} has requested to delete path ${path}`
    );

    // Run a recursive delete on the given document or collection path.
    // The 'token' must be set in the functions config, and can be generated
    // at the command line by running 'firebase login:ci'.
    return firebase_tools.firestore
      .delete(path, {
        project: process.env.GCLOUD_PROJECT,
        recursive: true,
        yes: true,
        token: functions.config().fb.token
      })
      .then(() => {
        return {
          path: path 
        };
      });
  });

I've also added the token to the configuration using : firebase functions:config:set fb.token="$FIREBASE_TOKEN" (where $FIREBASE_TOKEN is the token generated with firebase login:ci)

After deploying my functions with firebase deploy --only functions, I checked my Functions Overview to check that my newly created function was there. It was.

Now all I need to do is to called my function from my app with:

let path = "users/\(userID)"

functions.httpsCallable("recursiveDelete").call(["path": path]) { (result, error) in
   if let error = error as NSError? {
      if error.domain == FunctionsErrorDomain {
         let code = FunctionsErrorCode(rawValue: error.code)
         let message = error.localizedDescription
         let details = error.userInfo[FunctionsErrorDetailsKey]
         print("Code: \(code)")
         print("Message: \(message)")
         print("Details: \(details)")
      }
   }
}

When I called that function, the Xcode terminal prints this :

NSLocalizedDescription=The request timed out., NSErrorFailingURLStringKey=https://myapp.cloudfunctions.net/recursiveDelete, NSErrorFailingURLKey=https://myapp.cloudfunctions.net/recursiveDelete, _kCFStreamErrorDomainKey=4}

Code: Optional(__C.FIRFunctionsErrorCode)

Message: DEADLINE EXCEEDED

Details: nil

and in my Firestore Function Log panel, I have the following :

User ... has requested to delete path users/... where ... is the ID of the document

And then, Function execution took 540005 ms, finished with status: 'timeout'

I tried this, ie changing const path = data.path; to const path = `users/${context.auth.uid}`; but that didn't work either.

Does anybody know what the problem is?