Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires vimeo/psalm ^6.1.0 -> satisfiable by vimeo/psalm[6.1.0, 6.x-dev]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.6.0, ..., 4.x-dev, v5.0.0alpha1, ..., v5.4.0]. - Conclusion: don't install one of nikic/php-parser[v5.0.0alpha3], infection/infection[0.26.21] (conflict analysis result) - Conclusion: install nikic/php-parser v5.0.0alpha3 (conflict analysis result) - infection/infection 0.26.19 requires nikic/php-parser ^4.15.1 -> satisfiable by nikic/php-parser[v4.15.1, ..., 4.x-dev]. - Root composer.json requires infection/infection ^0.26.19 -> satisfiable by infection/infection[0.26.19, 0.26.20, 0.26.21, 0.26.x-dev]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.