The 403 signature mismatch error when uploading egress recordings to Supabase S3 is most commonly caused by incorrect URL formatting during request signing. For S3-compatible services like Supabase, you must set force_path_style to true in your S3 configuration. This ensures the bucket name is included in the path rather than as a subdomain, which is required for Supabase and many other non-AWS providers. To resolve this: • Set

force_path_style: true

in your S3Upload configuration. • Verify your endpoint matches the S3-compatible endpoint format provided by Supabase. • Double-check your access key, secret, region, and bucket name are correct and that your credentials have write permissions to the bucket. Example configuration:

const fileOutput = new EncodedFileOutput({
  filepath: `recording-${Date.now()}.mp4`,
  s3: new S3Upload({
    endpoint: '[your-supabase-s3-endpoint]',
    accessKey: '[your-access-key]',
    secret: '[your-secret-key]',
    region: '[your-region]',
    bucket: '[your-bucket-name]',
    force_path_style: true
  })
});

After making these changes, try the upload again. If the error persists, confirm your credentials and permissions, and ensure the endpoint URL is correct. Sources: Egress output types | LiveKit Docs | Egress & Recording | livekit/livekit_composite | DeepWiki