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.
Easily accept Bitcoin, Ethereum and many other crypto payments on your WHMCS website
Send account statements to customers
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.
Introduce extra billing models and charge your clients for actual server resource usage.
Introduce discounts applicable to orders of specified products combinations or quantities.