Warning: Undefined variable $conexion in /var/www/html/php/mod_fechas.php on line 4

Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in /var/www/html/php/mod_fechas.php:4 Stack trace: #0 /var/www/html/php/mod_fechas.php(4): mysqli_query() #1 {main} thrown in /var/www/html/php/mod_fechas.php on line 4