USSD failed with error

Fatal error: Uncaught exception 'Predis\Connection\ConnectionException' with message 'Error while reading line from the server. [tcp://127.0.0.1:6379]' in /tmp/web/www/cgi-bin/inc/predis/src/Connection/AbstractConnection.php:146 Stack trace: #0 /tmp/web/www/cgi-bin/inc/predis/src/Connection/StreamConnection.php(194): Predis\Connection\AbstractConnection->onConnectionError('Error while rea...') #1 /tmp/web/www/cgi-bin/inc/predis/src/Connection/AbstractConnection.php(134): Predis\Connection\StreamConnection->read() #2 /tmp/web/www/cgi-bin/inc/predis/src/Connection/AbstractConnection.php(126): Predis\Connection\AbstractConnection->readResponse(Object(Predis\Command\ListPopFirstBlocking)) #3 /tmp/web/www/cgi-bin/inc/predis/src/Client.php(328): Predis\Connection\AbstractConnection->executeCommand(Object(Predis\Command\ListPopFirstBlocking)) #4

/tmp/web/www/cgi-bin/inc/predis/src/Client.php(312): Predis\Client->executeCommand(Object(Predis\Command\ListPopFirstBlocking)) #5 /tmp/web/www/cgi-bin/php/sms-sender.php(570): Predis\Cl in /tmp/web/www/cgi-bin/inc/predis/src/Connection/AbstractConnection.php on line 146