Allow download from must be a valid mode
Saving Files settings failed because Link IP logic / “Allow download from” was not one of the allowed modes.
Why this happens
Admin-only validation on link_ip_logic. Allowed values: Exact IP, first-three octets, first-two octets, or All IPs (exact / first3 / first2 / all). Downloaders never see this string — they see IP mismatch messages when a link is bound and their IP does not match.
Diagnose and fix
1. Admin → Settings → Files → Link IP logic — pick one of the four modes and save again.
2. Do not POST arbitrary strings via API/scripts.
3. After save, new download links follow that binding rule.
4. End-user “wrong network” issues are a different message — adjust logic or recreate the link.