Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires eliashaeussler/phpstan-config ^2.0 -> satisfiable by eliashaeussler/phpstan-config[2.0.0, ..., 2.5.1]. - Root composer.json requires phpstan/phpstan-phpunit ^2.0 -> satisfiable by phpstan/phpstan-phpunit[2.0.0, 2.0.1]. - eliashaeussler/phpstan-config[2.0.0, ..., 2.5.1] require phpstan/phpstan ^1.9 -> satisfiable by phpstan/phpstan[1.9.0, ..., 1.12.10]. - phpstan/phpstan-phpunit[2.0.0, ..., 2.0.1] require phpstan/phpstan ^2.0 -> satisfiable by phpstan/phpstan[2.0.0, 2.0.1]. - You can only install one version of a package, so only one of these can be installed: phpstan/phpstan[1.7.15, ..., 1.12.10, 2.0.0, 2.0.1]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.