Laravel unserialize

I have PHP 7.1, Laravel 5.5 in my server. But when I try to start using this app I have error

unserialize(): Error at offset 0 of 320 bytes {"exception":"[object] (ErrorException(code: 0): unserialize(): Error at offset 0 of 320 bytes at /var/www/html/DS-v2.0-Front/vendor/laravel/framework/src/Illuminate/Encryption/Encrypter.php:149)"} []

What I can do to fix this error?

via Chebli Mohamed