Insufficient Funds: When the customer’s account lacks the necessary funds to cover the payment.

Account Closure: If the customer closes their account before the transaction is completed.

Invalid Account Number: When the provided account number is incorrect or improperly structured.

Unauthorized Transaction: Occurs when a payment intended for a business is mistakenly processed on a consumer account, or vice-versa.

Revoked Authorization: When the customer revokes permission for the transaction.

Payment Stop: When the customer stops the payment before it is processed.

Uncollected Funds: Happens when subsequent payments deplete the payer's account, leaving insufficient funds.

Customer Dispute: If the payer claims they don't recognize the merchant or didn't authorize the debit.

Legal Action: Account freezing due to legal actions like tax liens or settlements.

Non-Transaction Account: When the customer uses a non-transaction account for the payment, such as a money market deposit account.