Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpstan/phpstan ^2.1 -> satisfiable by phpstan/phpstan[2.1.0, ..., 2.1.16]. - phpstan/phpstan[2.1.0, ..., 2.1.16] require php ^7.4|^8.0 -> your php version (7.3.33) does not satisfy that requirement.