Sign in again to upload
The browser uploader got 401 from upload init and maps that to “You need to sign in again to upload.”
Why this happens
The member cookie/session is missing, expired, or invalid when /api/upload/init (or a related start call) runs. This is not the same as CSRF invalid (usually 403) or “Could not load security token.”
Diagnose and fix
1. Member: sign out and sign in, then open /upload again with cookies allowed.
2. Avoid private-mode quirks that drop cookies mid-batch; keep one tab signed in.
3. API automation should use a Member API key, not a stale browser session.
4. If CSRF fails separately, refresh the page or see Could not load security token.