Apart from insufficient funds, there are various reasons why your payment could have failed.
The most common reasons are:
The credit card linked to your account has expired. This might have happened a while ago, so please make sure you update your card details on your User Profile (please remove your old card first, then add a new card). Transactions are still being run on knowingly expired cards as some financial institutions will still approve transactions with expired cards.
Bank's fraud rules blocked the transaction
This could be based on your location or based on previous transactions on your account, which make it seem that this transaction might be fraud. You will need to contact your bank for more information.
Possible Lost or Stolen Card
You might have lost your card a while ago and you might already have gotten a replacement card. However, your card details linked to your Sherpa account are not updated yet (please remove your old card first, then add a new card). If you did not lose your card, the card used has likely been reported as lost. You will need to contact your bank for more information.
Your bank declined the transaction, typically because the card in question does not support this type of transaction – for example, you used an FSA debit card for a non-healthcare related purchase. You will need to contact your bank for more information.
If you are not using a credit card, but PayPal to pay your balance, you will need to contact Paypal to find out why the payment of your balance failed.