Quick summary

Before your photos upload, Imagen uploads your project file (for example, your Lightroom Classic catalog). That upload didn't finish.

How to fix this

1. Click Try again. Short connection drops are the most common cause.
2. Use a stable connection, and turn off any VPN or proxy while you upload.
3. Make sure your firewall or antivirus isn't blocking Imagen.
4. Keep your catalog on your computer's local drive, not a network drive or a cloud-synced folder (Dropbox, iCloud, OneDrive, Google Drive).
5. Very large catalogs take longer to upload. In Lightroom Classic, go to File › Optimize Catalog, and try again.