"Video length exceeds limit" — >15 min without channel verification. Verify at YouTube Studio.
"Aspect ratio invalid for Shorts" — Shorts require 9:16. Re-crop in the editor.
"Quota exceeded" — very rare; YouTube's daily upload API quota. Retry the next day.
"Copyright-claim detected" — YouTube's Content ID flagged music or footage. Swap the music (editor → Music).
TikTok
"Sandbox mode" — until TikTok's audit approves direct-post, uploads land as drafts in the TikTok app. Not a failure — open the TikTok app and tap Post.
"Video too long" — >10 min.
"Duplicate content" — TikTok blocks repeats within ~24h.