Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^11.0.0 -> satisfiable by phpunit/phpunit[11.0.0, ..., 11.4.3]. - Root composer.json requires psalm/plugin-phpunit ^0.18.4 -> satisfiable by psalm/plugin-phpunit[0.18.4]. - vimeo/psalm[5.17.0, ..., 5.21.1] require nikic/php-parser ^4.16 -> satisfiable by nikic/php-parser[v4.16.0, ..., v4.19.4]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.16.0, ..., v4.19.4, v5.0.0, ..., v5.3.1]. - Conclusion: install nikic/php-parser v5.3.1 (conflict analysis result) - Conclusion: don't install nikic/php-parser[v5.3.1] | install one of vimeo/psalm[5.17.0, ..., 5.21.1] (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.