Why does the repayment reminder message sent by China Everbright Bank prompt "insufficient account balance"?

Everbright Bank will compare the balance in the customer's repayment account with the repayment amount five days before the deduction date. If the amount is insufficient, it will send a reminder message. As the balance of repayment account may change every day, Everbright Bank will indicate the date when the balance is judged to be insufficient in the news.