Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires dms/phpunit-arraysubset-asserts dev-master -> satisfiable by dms/phpunit-arraysubset-asserts[dev-master]. - dms/phpunit-arraysubset-asserts dev-master requires phpunit/phpunit ^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0 || ^10.0 -> found phpunit/phpunit[4.8.36, 5.7.21, ..., 5.7.27, 6.0.0, ..., 6.5.14, 7.0.0, ..., 7.5.20, 8.0.0, ..., 8.5.41, 9.0.0, ..., 9.6.22, 10.0.0, ..., 10.5.45] but it conflicts with your root composer.json require (^12). Problem 2 - Root composer.json requires friendsofphp/php-cs-fixer 3.65.0 -> satisfiable by friendsofphp/php-cs-fixer[v3.65.0]. - Root composer.json requires phpunit/phpunit ^12 -> satisfiable by phpunit/phpunit[12.0.0]. - friendsofphp/php-cs-fixer v3.65.0 requires 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]. - 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. - 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].