Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^12.0.0 -> satisfiable by phpunit/phpunit[12.0.0]. - Root composer.json requires slam/php-cs-fixer-extensions ^3.12.0 -> satisfiable by slam/php-cs-fixer-extensions[v3.12.0]. - friendsofphp/php-cs-fixer[v3.64.0, ..., v3.66.0] require sebastian/diff ^4.0 || ^5.0 || ^6.0 -> satisfiable by sebastian/diff[4.0.0, ..., 4.0.6, 5.0.0, ..., 5.1.1, 6.0.0, 6.0.1, 6.0.2]. - friendsofphp/php-cs-fixer[v3.66.1, ..., v3.68.5] require sebastian/diff ^4.0 || ^5.1 || ^6.0 -> satisfiable by sebastian/diff[4.0.0, ..., 4.0.6, 5.1.0, 5.1.1, 6.0.0, 6.0.1, 6.0.2]. - phpunit/phpunit 12.0.0 requires sebastian/diff ^7.0.0 -> satisfiable by sebastian/diff[7.0.0]. - sebastian/diff[4.0.0, ..., 4.0.1] require php ^7.3 -> your php version (8.3.16) does not satisfy that requirement. - slam/php-cs-fixer-extensions v3.12.0 requires friendsofphp/php-cs-fixer ^3.64.0 -> satisfiable by friendsofphp/php-cs-fixer[v3.64.0, ..., v3.68.5]. - You can only install one version of a package, so only one of these can be installed: sebastian/diff[4.0.0, ..., 4.0.6, 5.0.0, ..., 5.1.1, 6.0.0, 6.0.1, 6.0.2, 7.0.0].