STEP 1: The first thing to check is that you are actually connected under the Integrations tab.
STEP 2: Watch the video below to make sure you have your campaign set up correctly.
If you've already watched the video and just need a quick reminder/checklist here it is...
Check Integrations and disconnect/reconnect to the social network that's failing to post
On the campaign Set Up tab, check the social network toggle is set to Active
Make sure the start date is after today
Make sure the end date is after the start date and is set to the right number of days in the future (calculated by number of active posts / divided by post frequency)
Make sure there is text in the text box for each social network you're posting to, on every active post (if post text is missing for example in one of the Instagram boxes, and you've asked the system to post to Instagram, this will stall the campaign)
[This won't stop a campaign but it will affect the timings] Make sure your time zone is set correctly under the Profile tab in the My Account area
If everything is set correctly, and your posts still aren't posting, don't get frustrated, just raise a ticket using the chat tool on this page.