Im starting to find it comical that WHMCS pays no attention to the tax laws in the US where their biggest market is. By not making configurable options be their own line item on the invoice and have the ability to make them individually taxable, that are putting many US hosting companies in violation of local tax laws.
You might say use Addons instead of configurable options. The issues is Addons do not allow quantities.
But for example, in TN, AZ and GA, we are support to charge sales tax on any software license we sell. We need quantities for things like Microsoft CAL Licenses.
I know many other states have this same law, including Texas where WHMCS is located. But WHMCS does even collect sales tax on their licenses, even though they should if the software is being installed on a server in TX. Maybe turning them into the Texas Sec of State, so they are audited will get their attention on the fact they need to fix this.