#ErrorLog [fixed] Server sent charset (255) unknown to the client – MySQL

Its happend because it has different charset in server and what we need in apps. So, to fixing this problem, we should update mysql configuration in our server, open your mysql.cnf, bcs I using Linux, then my mysql.cnf is located at /etc/mysql/mysql.cnf. Move to that directory using cd /etc/mysql/mysql.cnf

Then open using, sudo nano mysql.cnf and at the end of the file, add some following code:

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8

[mysqld]
collation-server = utf8_unicode_ci
character-set-server = utf8
default_authentication_plugin = mysql_native_password

restart mysql using systemctl restart mysql or sudo services mysql restart, and try to open your app again.