Your requirements could not be resolved to an installable set of packages. Problem 1 - infection/infection 0.29.8 requires nikic/php-parser ^5.0 -> satisfiable by nikic/php-parser[v5.0.0, ..., v5.3.1]. - vimeo/psalm[5.15.0, ..., 5.26.1] require php ^7.4 || ~8.0.0 || ~8.1.0 || ~8.2.0 || ~8.3.0 -> your php version (8.4.0RC1) does not satisfy that requirement. - Root composer.json requires infection/infection 0.29.8 -> satisfiable by infection/infection[0.29.8]. - vimeo/psalm 4.30.0 requires nikic/php-parser ^4.13 -> satisfiable by nikic/php-parser[v4.13.0, ..., v4.19.4]. - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.17.0, ..., v4.19.4, v5.0.0, ..., v5.3.1]. - Root composer.json requires vimeo/psalm ^4.30.0 || ^5.15 -> satisfiable by vimeo/psalm[4.30.0, 5.15.0, ..., 5.26.1]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.