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]. - Root composer.json requires vimeo/psalm ^6.8.5 -> satisfiable by vimeo/psalm[6.8.5, 6.8.6]. - vimeo/psalm[6.8.5, ..., 6.8.6] require nikic/php-parser ^5.0.0 -> satisfiable by nikic/php-parser[v5.0.0, ..., v5.4.0]. - Conclusion: don't install nikic/php-parser v5.4.0 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.