Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires psalm/plugin-phpunit ^0.19.0 -> satisfiable by psalm/plugin-phpunit[0.19.0]. - vimeo/psalm[5.1.0, ..., 5.13.1] require php ^7.4 || ~8.0.0 || ~8.1.0 || ~8.2.0 -> your php version (8.3.15) does not satisfy that requirement. - Root composer.json requires phpunit/phpunit ^11.0.0 -> satisfiable by phpunit/phpunit[11.0.0, ..., 11.5.2]. - vimeo/psalm 5.26.0 requires nikic/php-parser ^4.17 -> satisfiable by nikic/php-parser[v4.17.0, ..., v4.19.4]. - vimeo/psalm[5.14.0, ..., 5.25.0] require nikic/php-parser ^4.16 -> satisfiable by nikic/php-parser[v4.16.0, ..., v4.19.4]. - Conclusion: don't install one of nikic/php-parser[v5.4.0], vimeo/psalm[5.26.1] | install nikic/php-parser[v4.17.0] (conflict analysis result) - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.13.0, ..., v4.19.4, v5.0.0, ..., v5.4.0]. - Conclusion: install nikic/php-parser v5.4.0 (conflict analysis result) - Root composer.json requires vimeo/psalm ^5.1 -> satisfiable by vimeo/psalm[5.1.0, ..., 5.26.1]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.