Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpstan/phpstan-phpunit ^1.4.1 -> satisfiable by phpstan/phpstan-phpunit[1.4.1, 1.4.2, 1.4.x-dev]. - phpstan/phpstan-phpunit[1.4.1, ..., 1.4.x-dev] require phpstan/phpstan ^1.12 -> found phpstan/phpstan[1.12.0, ..., 1.12.x-dev] but it conflicts with your root composer.json require (^2.1.2). Problem 2 - Root composer.json requires phpstan/phpstan-strict-rules ^1.6.1 -> satisfiable by phpstan/phpstan-strict-rules[1.6.1, 1.6.2, 1.6.x-dev]. - phpstan/phpstan-strict-rules[1.6.1, ..., 1.6.x-dev] require phpstan/phpstan ^1.12.4 -> found phpstan/phpstan[1.12.4, ..., 1.12.x-dev] but it conflicts with your root composer.json require (^2.1.2). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.