Open the Post → per-target row shows the friendly error + underlying platform code.
Common reasons:
- Token expired → reconnect from Connections.
- Media too large / wrong aspect → our transcoder tried but couldn't fit; open the composer and use the crop / pad options.
- Duplicate content → some platforms (esp. TikTok) reject identical uploads.
- Business/Personal mismatch → IG Personal accounts can't use tagging, first-comment hashtags, or location.
Always safe to Retry from the row's ⋯ menu.