Ok let me preface that this is of no fault of WHMCS but my own. However I thought it might be a worthwhile addition to the software.
Making it short here. I had a client whose invoice had just been generated. Then there was an issue with a false positive on a scan I ran which removed a file from his site(a known issue but I forgot to include the excludes file to the scan). He caught it 12 hours later and so I issued him a credit for the next month to be free. I hadn't realized the invoice had already been generated(as I said an oversight on my part). So tonight he was suspended for non-payment but luckily I caught it in my email sent to my phone 10 minutes after it happened. He was "luckily" understanding over the matter.
So I was thinking maybe a check could be run before an account is suspended to see if the users credit amount has changed? This could also be useful not just for a stupid mistake like I made but also if a customer was to just deposit a larger amount of money(than the due invoice say to pay for 3 months ahead) into his account assuming it would take care of a due invoice already.
Well thanks for reading. Either way I myself will be more careful