When a Series can't render or post, it skips the slot and tries the next one. The Series page shows a note with the reason. The common ones:
Not enough credits. The post cost more than your remaining balance. Top up a pack, upgrade, or wait for the monthly reset. The Series resumes on its own at the next slot.
Channel needs reconnecting. YouTube access expired or was revoked. Reconnect under Settings → Channels.
Still on trial. Scheduled posting starts once you're on a plan.
Plan limit. For example the plan's parallel render limit was full at render time, or the Series no longer fits the plan after a downgrade.
Waiting for your approval. On manual approval, the post rendered fine and is sitting in review. Approving it publishes it.
Fix the cause and the Series carries on by itself. Skipped slots are never posted late.
If the note on the Series page doesn't match any of these, email [email protected] and a human will read it.