Allow clients to increase disk space themselves
Clients regularly fill their disk quota. It would be nice if they could log into WHMCS, select additional disk space add-ons (not just upgrade their hosting package), be billed, and have their disk space increased accordingly. We sell a lot of disk space ala carte.
Currently we've tried a few things in WHMCS. Creating our own add-on, even a disk space package, but in the end, we have to increase their disk space manually on the hosting control panel.