Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^13.0 -> satisfiable by phpunit/phpunit[13.0.0, ..., 13.3.x-dev (alias of dev-main)]. - phpunit/phpunit[dev-main, 13.0.0, ..., 13.3.x-dev] require php >=8.4.1 -> your php version (8.3.31) does not satisfy that requirement. - phpunit/phpunit 13.3.x-dev is an alias of phpunit/phpunit dev-main and thus requires it to be installed too.