Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires vimeo/psalm ^5.26 -> satisfiable by vimeo/psalm[5.26.0, 5.26.1, 5.x-dev]. - Root composer.json requires phpunit/phpunit ^11.0.0 -> satisfiable by phpunit/phpunit[11.0.0, ..., 11.5.x-dev]. - Root composer.json requires psalm/plugin-phpunit ^0.19.0 -> satisfiable by psalm/plugin-phpunit[0.19.0]. - psalm/plugin-phpunit 0.19.0 requires vimeo/psalm dev-master || ^5@beta || ^5.0 -> satisfiable by vimeo/psalm[5.26.0, 5.26.1, 5.x-dev]. - vimeo/psalm[5.26.0, ..., 5.x-dev] require nikic/php-parser ^4.17 -> satisfiable by nikic/php-parser[v4.17.0, ..., 4.x-dev]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.0.0alpha1, ..., 4.x-dev, v5.0.0alpha1, ..., v5.4.0]. - Conclusion: install nikic/php-parser v5.4.0 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.