Temporary problems (network outage, rate limit) are retried automatically with increasing delays — up to five times over about two hours. Problems that need a person stop immediately and tell you what to change:

• Authorization expired / permission denied → reconnect the channel; its other scheduled posts are paused meanwhile.
• Rejected content (e.g. "Instagram does not accept PNG images", "duplicate post") → edit the post and reschedule.
• Daily limits (Instagram 50 posts/day, YouTube upload quota) → retried after the limit resets.

Failed posts live under Publishing → Failed; the calendar item is red. "Retry now" reschedules it two minutes out.