Set up a Cloud Storage lifecycle policy to automatically delete objects after 45 days.

Generate signed URLs for users, granting them temporary access to upload and access their invoices for a limited time.

Configure an SFTP server with individual user accounts for each supplier to manage invoice uploads.

Implement a Cloud Function that triggers after 45 days to delete expired invoice objects.

Create a script to periodically scan and delete Cloud Storage buckets older than 45 days.