Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpstan/phpstan-phpunit ^1.4 -> satisfiable by phpstan/phpstan-phpunit[1.4.0]. - phpstan/phpstan-phpunit 1.4.0 requires php ^7.2 || ^8.0 -> your php version (7.1.33) does not satisfy that requirement. Problem 2 - Root composer.json requires phpstan/phpstan-strict-rules ^1.6 -> satisfiable by phpstan/phpstan-strict-rules[1.6.0]. - phpstan/phpstan-strict-rules 1.6.0 requires php ^7.2 || ^8.0 -> your php version (7.1.33) does not satisfy that requirement. Problem 3 - phpstan/extension-installer[1.4.0, ..., 1.4.1] require php ^7.2 || ^8.0 -> your php version (7.1.33) does not satisfy that requirement. - Root composer.json requires phpstan/extension-installer ^1.4 -> satisfiable by phpstan/extension-installer[1.4.0, 1.4.1].