Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires infection/infection ^0.27.11 -> satisfiable by infection/infection[0.27.11]. - Conclusion: don't install nikic/php-parser v4.15.1 (conflict analysis result) - Root composer.json requires vimeo/psalm ^6.0.0 -> satisfiable by vimeo/psalm[6.0.0]. - infection/infection 0.27.11 requires nikic/php-parser ^4.15.1 -> satisfiable by nikic/php-parser[v4.15.1, ..., v4.19.4]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.15.1, ..., v4.19.4, v5.0.0, ..., v5.4.0]. - vimeo/psalm 6.0.0 requires nikic/php-parser ^5.0.0 -> satisfiable by nikic/php-parser[v5.0.0, ..., v5.4.0]. - Conclusion: don't install nikic/php-parser v5.0.0 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.