"An error has occurred. To try again, reload the page and start the workflow."
I've been looking for answers and as many have suggested, I've restarted services, recycling pools and Workflow Manager, but here's the seemingly unique problem at my end.
Even though service bus is installed according to the Web Platform Installer, the service bus AND Service Gateway Services are NOT listed under Services. It's like they're not installed.
Workflow server status – Workflow is connected
Both Workflow Service Application and Workflow service application proxy Are started".
Snapshot of what I get when I try to execute a SharePoint 2013 approval