If you noticed an error status of your campaign like on the picture below.
You need to check the statuses of the sending accounts connected to this campaign. This error happens because all of the sending email accounts ran into a temporary error with their SMTP, which lead to automatically pausing the campaign.
To fix this issue, do the following steps.
On your Instantly Dashboard, navigate to Email Accounts tab.
On your dashboard, you can see if there are any other error status.
If you see no errors or disconnects, relaunch the campaign by pressing the Start button.