Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires vimeo/psalm ^6.11 -> satisfiable by vimeo/psalm[6.11.0]. - vimeo/psalm 6.11.0 requires php ~8.1.31 || ~8.2.27 || ~8.3.16 || ~8.4.3 -> your php version (8.1.19) does not satisfy that requirement. Problem 2 - Root composer.json requires psalm/plugin-phpunit ^0.19.5 -> satisfiable by psalm/plugin-phpunit[0.19.5]. - psalm/plugin-phpunit 0.19.5 requires vimeo/psalm dev-master || ^6.10.0 -> satisfiable by vimeo/psalm[6.11.0]. - vimeo/psalm 6.11.0 requires php ~8.1.31 || ~8.2.27 || ~8.3.16 || ~8.4.3 -> your php version (8.1.19) does not satisfy that requirement.