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.
Easily accept Bitcoin, Ethereum and many other crypto payments on your WHMCS website
Send account statements to customers
Allow Clients to cancel fund invoices & automated cancellations of fund invoices
As WHMCS does provide tax rules options where you can configure your GST tax but we have some extra features in our module that makes it stand out and necessary to use.