You can send one of these reminders manually but only if one is due. So if the invoice is appearing on the credit control list you can pop open the preview dialogue and select the template.
At the moment there’s no way to send these ad-hoc.
We may be able to look at including these templates in the general invoice preview screen (i.e.) where you send the invoice originally. I’d need to consult on that.
Although there would be nothing to see as no reminders would have been triggered, hence why we don’t show a link anywhere.
Suggestion
If you want to force a reminder to be triggered you can locate the invoice on the main invoice list and click on the hour glass icon.
You can then change the schedule manually. If you make a change though, give the system 5 mins to trigger the alert and then you should see that red box in the dashboard.