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, 12.0.1]. - Root composer.json requires vimeo/psalm ^5.25 -> satisfiable by vimeo/psalm[5.25.0, 5.26.0, 5.26.1]. - phpunit/phpunit[12.0.0, ..., 12.0.1] require 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. - vimeo/psalm[5.25.0, ..., 5.26.1] 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]. - You can only install one version of a package, so only one of these can be installed: sebastian/diff[1.1.0, ..., 1.4.3, 2.0.1, 3.0.0, ..., 3.0.6, 4.0.0, ..., 4.0.6, 5.0.0, ..., 5.1.1, 6.0.0, 6.0.1, 6.0.2, 7.0.0]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.