latest Update 2021

Create a custom module.  Let’s call it Ankur_Pay.  Create these files:  app/etc/module/Custom_Pay.xml with this content  <?xml version = "1.0" ?> < config >     < modules >         < Ankur_Pay >             < active > true </ active >             < codePool > local </ codePool >             < depend >< Mage_Payment  />< Mage_Paypal  /></ depend > <!-- add here all the payment modules you have so this module will be loaded last -->         </ Ankur_Pay >     </ modules > </ config > app/code/local/Custom/Pay/etc/config.xml  <?xml version = "1.0" ?> < config >     < modules >         < Ankur_Pay >             < version > 0.1.0 </ version >         </ Ankur_Pay >     </ modules > </ config > app/code/local/Custom/Pay/etc/system.xml  <?xml version = "1.0" ?> < config >     < sections >

Open libraries/Input.php (system/core/Input.php in CI version 2.0+) and locate function _clean_input_keys($str){, The whole block should look like so: function _clean_input_keys($str) {     if ( ! preg_match("/^[a-z0-9:_\/-]+$/i", $str))     {         exit('Disallowed Key Characters.');     }     return $str; } Modify the PCRE sot that it allows the new chars. Please not that the char thats missing is the .(dot) and you should always escape the .(dot) in Regular Expressions as they will otherwise allow any single char. /^[a-z0-9:_\/-\.]+$/i