Message failure issue with Postmark

[Chillifish]

I don't know if anyone can help. I have Postmark managing my unsubscribes for a particular workspace. The sendportal API doesn't process the webhook, so I have to unsubscribe them manually. Inevitably I occasionally miss one or two. If an address is rejected by Postmark during a campaign send, it throws an error and the campaign just sticks on 'sending' forever.

Is anyone familiar enough with the code to let me know if there's a way I can restart the campaign. Perhaps somewhere in the database there might be a list of the emails that are yet to be sent out?