Would it be possible to send the email out, that advises of insufficient funds, the day prior to requiring those funds?
I know many will have a handle on the required level of funding but I have clients that don't even look at their account and rely on us to advise the amount they need to pay into Telleroo to ensure payments are made. When they forget to do this, they find themselves with bills unpaid on the day they are supposed to be in other people's accounts - not so much of a fun conversation when it's employee's wages that are potentially late!
Faster payments are all we'll and good but not all banks can cope with this on weekends and bank hols... Could you send the email the previous day or 24 hours earlier?