Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^13.0.0 -> satisfiable by phpunit/phpunit[13.0.0, 13.0.1]. - Root composer.json requires vimeo/psalm ^4.30.0 -> satisfiable by vimeo/psalm[4.30.0]. - phpunit/phpunit[13.0.0, ..., 13.0.1] require sebastian/diff ^8.0.0 -> satisfiable by sebastian/diff[8.0.0]. - Conclusion: don't install sebastian/diff 8.0.0 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.