Recurring Billing and invoice Validation
It seems to be a common and recurring issue that I have experienced many times with multiple WHMCS installs, that next due dates can end up out of sync due to not being updated, which can result in customers being suspended for non payment even when they have paid, or invoices no longer being generated.
There really needs some for of validation checks done to detect these problems and take action or open a ticket to resolve them.
Checking that recurring invoices are correctly being generated and none have been skipped.
check that next due dates have been updated correctly.
One of the causes I only recently discovered is if an automatic payment fails, and you apply the payment manually, the next due date is not updated. I can imagine a lot of people either do not know this, or even if they do know, forget to manually update the next due date, especially considering the people who handle billing are usually non technical.