The simple module allows showing Credit history so they can keep their eye on how the credits are being applied.
The best place to start if you need help with a specific product is to contact the developer. All WHMCS Marketplace developers have both a website and support URL listed.
CleanHTML Invoice and Quote Free template.
The definitive solution for all your billing needs plus a lot of additional features
Automatically pay commissions to your salespeople, resellers etc.
Introduce extra billing models and charge your clients for actual server resource usage.
Send account statements to customers