CORS errors usually happen because the project is missing a web platform that allows the app to connect to it. To add a web platform:

1. Open your project in the Appwrite Console
2. Scroll down to the Integrations section
3. Click the Add platform button
4. Select Web app
5. Enter the hostname for your app

Besides the web platform, other reasons you may get this error are:

1. lack of access due to permissions on the bucket or file
2. incorrect project, bucket, or file id

Reference: https://appwrite.io/blog/post/cors-error