Declined Transactions are the ones shown with a RED DEC.
Decline reasons are various and whenever they are known, they are displayed in the Transaction Response Tab
There also exist Generic Declined - which are declines without a specified reason. These declines do have a reason, but the reason is not known to us or not disclosed. It is our suggestion that for such cases you refer the cardholder to call his bank (bank which issued the card) and they may be able to give the cardholder the specific reason or hints about why the transaction was declined.