Logic in ordering form fields
The thing I miss the most after moving to WHMCS from my previous billing system and the thing that makes WHMCS rather poor for advanced offering is that is misses logic feature in order fields.
WHMCS has configurable options, but they lack logic to hide/show or change other options which is called logic. Example, if I select drop down field 1, hide dropdown an checkfield 2 and 3. If I click the radio button A, show the hidden field 7.
Example, I was able to replicate the server/vps ordering forms using the configurable options. You can put all the dropdown, checkboxes, etc (the slider which is in the documentation was never to bee seen) but they are most useless for a real server order form because options are usually invalidated or validated depending on what the customer selected previously.
Example, you make a field with OS selection, a field with software, control panel, etc. The customer then selects Windows Server as his main operating system choice and then selects cPanel as control panel. You see the problem here? They are incompatible. The field logic in my previous billing systems automatically hided the cPanel option when someone selected a Windows option or Ubuntu or any OS not supported by cPanel.
The same is true for example if someone selects a RAM variable or a processor variable, some softwares are licensed per core you need to hide the options or and show another with a higher or lower price, or some software may not work with less than XX ram so you need to hide that if customers select the lowest ram option. Same for network, someone selects a speed port and you need to hide the transfer option as now its unmetered. I could go on and on, but basically without logic in the configurable options, its very hard to impossible to offer any VPS/Cloud/Server order form which provides customers some options.
Since this options are actually called "configurable" they should allow the customer to configure his services options. I will not mention which was the other billing software that had this, but I assume WHMCS can find that on its own.
This is the only thing I find WHMCS is lacking for a VPS/Cloud/Server ordering platform. If logic is implemented with this field, and you can in the future pass variables from them based on the options selected, a user can create any order form as basic or complex as they want for any type of offering.