Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^11.0 -> satisfiable by phpunit/phpunit[11.0.0]. - psalm/plugin-phpunit 0.18.4 requires vimeo/psalm dev-master || dev-4.x || ^4.7.1 || ^5@beta || ^5.0 -> satisfiable by vimeo/psalm[5.8.0, ..., 5.21.1]. - vimeo/psalm[5.8.0, ..., 5.21.1] require sebastian/diff ^4.0 || ^5.0 -> satisfiable by sebastian/diff[4.0.0, ..., 4.0.5, 5.0.0, ..., 5.1.0]. - You can only install one version of a package, so only one of these can be installed: sebastian/diff[4.0.0, ..., 4.0.5, 5.0.0, ..., 5.1.0, 6.0.0]. - phpunit/phpunit 11.0.0 requires sebastian/diff ^6.0 -> satisfiable by sebastian/diff[6.0.0]. - Root composer.json requires psalm/plugin-phpunit ^0.18.4 -> satisfiable by psalm/plugin-phpunit[0.18.4]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.