In two lines: if a post didn't go out, it's almost always because the account needs to be reauthorized, the post didn't reach the Published status, or the format wasn't compatible. Check these causes in order.
Is the network account connected?
If in Settings > Integrations the platform shows a Pending permissions chip or an expired-connection warning, the post won't go out until you renew the access. See Reauthorize an integration.
Did the post reach the Approved status and get scheduled?
A post in Draft or Pending doesn't publish on its own. Make sure it's Approved and scheduled with a future date and time. If the date already passed while it was under review, schedule it again.
Is the format compatible with the platform?
Each network has its requirements. If the format or size don't meet that platform's specifications, the post may fail. See Formats and requirements per platform.
Open the List view in the Planner to see the status of each post at a glance and identify the ones that were left unpublished.
Still have questions?
Ask MIA, the MB Suite AI assistant: open it with the MB AI button (⌘J) in the top bar. MIA knows the section you're in, so you can ask it directly about what you see on screen.