There are a number of reasons a credit card payment might not go through even though the card used is valid and has the available funds. The most common are someone incorrectly entering the card number, expiration date or CVV code, or not entering the same address the credit card company has on file for the account.
If a member is having trouble making a payment you can see what the problem is by logging into your ECRYPT account and clicking on Credit Cards. On that screen you can select the date range, select Status from the drop down menu and Declined as the status.
The Result screen will look like this:
In this example you can see that the customer attempted to submit payment three times and each time the transaction was declined. Click on the Transaction ID and you'll see the full details of the transaction including the reason it was declined.
In this case the card was declined by the issuer and there wasn't further information provided. That could be due to insufficient funds; a security check (maybe this got flagged as a suspicious transaction); etc. If the reason was an invalid number, for example, that would be indicated here.
Remind your members that each time they try to make a payment the card is authorized. That means that a transaction is run to verify that the card is valid and has enough funds for the charge. Each time your members tries to submit a payment (and its declined), the authorization shows on their account. It may Look like several charges are places but they are not "charges" they are just "authorizations".
Authorizations stay in the system for about 24 hours. Be clear with your members regarding the difference between "charges" and "authorizations", should have they have a declined transaction. (i.e. declined the charges are not processed and those authorizations drop off automatically at the end of the day)