That definitely helped. I actually found a location in the permissions where it was not correct - it looked different from where we were before (I don't recall where that was). I went to [Administration > Administration > Roles > End User > End User > Privileges > Modules > Incident Management > Process Related Objects > Incident] where I found the action listed with Read and Update, no Execute. I enabled Execute, End Users can now see the action.
Upon executing the action, which does move the process forward (resolves the incident, actually), I get a new error:
Privilege required. User enduser is not a member of a role or group with the Read privilege for the Lifecycle -> Non-Process Related Objects -> Response Level -> Status Escalation object. Please contact your system administrator.
I went to [...Modules > Lifecycle > Non-Process Related Objects] where I found both "Response Level" and "Status Escalation". Response Level is green for Read and Update; everything else is denied.
Any remarks on what permissions would need to change to permit this action for the End User role, and what any further implications might be at that point?
Thank you!