Answer: Prefer public HTTPS CDN/S3 URLs. Use
proxyDownload (or Drive/Dropbox auto mode) when the platform cannot fetch the source. Videos/Reels may still use resumable uploads after Postifys downloads the file.What this means in a real publishing workflow
A media URL is convenient only when both Postifys and the destination network can fetch it. Login pages, expiring signatures, blocked hotlinks, redirects, and HTML download pages commonly look like valid links but fail during publishing.
Recommended implementation
- Test the URL without browser cookies and confirm it returns the media bytes directly.
- Check the Content-Type and final response after redirects.
- Use Postifys proxy download when the provider cannot fetch the source reliably.
- Regenerate short-lived URLs immediately before queued publishing.
How to verify the fix
Google Drive and Dropbox sharing pages are not the same as direct media URLs. For large YouTube files, allow enough download time and keep the source available until the upload has finished.
Operational check: Test with one item, confirm the final destination and Postifys history state, and only then enable the recurring workflow. Keep the returned Postifys ID beside the source row so every result remains traceable.
Related Postifys resources
API documentation · Error reference · n8n automation guide · Safe retry guide · Compatibility matrix