OnlineNic refuse to make one:
And there's not one yet for Blesta. You can +1 the feature: https://requests.blesta.com/topics/idea/status/all/category/all/sort/all/page/5
I get this a lot mate:
Auto apply late fee for invoices
Automatically apply late fee for invoices that are past due.
Task Last Ran: 15 Jun 2017 12:23:18 PM Clear Task Lock
It all depends on the control panel you have...
cPanel = you need to do it via EasyApache and the Pecl addons.
Non panel = yum install php-pecl-mailpharse -y
It sounds like the currency values aren't correct because it thinks the credits are less than the total for the invoice so it wants you to check a gateway for the remainder.