Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires vimeo/psalm 5.20.0 -> satisfiable by vimeo/psalm[5.20.0]. - vimeo/psalm 5.20.0 requires nikic/php-parser ^4.16 -> found nikic/php-parser[v4.16.0, ..., 4.x-dev] but it conflicts with your root composer.json require (^5.0.0). Problem 2 - roave/infection-static-analysis-plugin[1.34.0, ..., 1.35.x-dev] require vimeo/psalm ^4.30.0 || ^5.15 -> satisfiable by vimeo/psalm[5.20.0]. - vimeo/psalm 5.20.0 requires nikic/php-parser ^4.16 -> found nikic/php-parser[v4.16.0, ..., 4.x-dev] but it conflicts with your root composer.json require (^5.0.0). - Root composer.json requires roave/infection-static-analysis-plugin ^1.34.0 -> satisfiable by roave/infection-static-analysis-plugin[1.34.0, 1.34.x-dev, 1.35.x-dev]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.