Invalid upload part
Chunked upload rejected a part because the part index / total-parts metadata does not make sense.
Why this happens
Parts are only valid when partIndex sits inside the range agreed at init (totalParts, chunkSize, totalBytes). An out-of-range index or inconsistent split produces “Invalid upload part” (or related API codes).
Live part routes more often return clearer cousins such as “Invalid partIndex,” “Part size mismatch…,” or “Missing part N.” Treat this family as bad chunk metadata or a stale upload session.
Diagnose and fix
1. Cancel the stuck upload and start a new upload (fresh init) so part indexes reset.
2. Confirm Mods → Desktop uploader (toggle.m_z) for browser chunks, or Member API upload mod for API clients.
3. API clients: ensure each PUT …/part?fileId=&partIndex= matches the init totalParts and byte sizes.
4. If many users fail at once, check disk/permissions on UPLOAD_DIR (see Could not save upload part) and proxy body limits.