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]. - vimeo/psalm 6.1.0 requires nikic/php-parser ^5.0.0 -> found nikic/php-parser[v5.0.0, ..., v5.4.0] but it conflicts with your root composer.json require (^4.19.1). Problem 2 - vimeo/psalm 6.1.0 requires nikic/php-parser ^5.0.0 -> found nikic/php-parser[v5.0.0, ..., v5.4.0] but it conflicts with your root composer.json require (^4.19.1). - php-standard-library/psalm-plugin 2.3.0 requires vimeo/psalm >=5.16 -> satisfiable by vimeo/psalm[6.1.0]. - Root composer.json requires php-standard-library/psalm-plugin ^2.3.0 -> satisfiable by php-standard-library/psalm-plugin[2.3.0]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.