Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires drupol/php-conventions ^6 -> satisfiable by drupol/php-conventions[6.0.0]. - drupol/php-conventions 6.0.0 requires vimeo/psalm ^5 -> found vimeo/psalm[5.0.0, ..., 5.26.1] but it conflicts with your root composer.json require (^6). Problem 2 - Root composer.json requires amphp/parallel-functions ^1 -> satisfiable by amphp/parallel-functions[v1.0.0, v1.1.0]. - Root composer.json requires vimeo/psalm ^6 -> satisfiable by vimeo/psalm[6.0.0]. - amphp/parallel-functions[v1.0.0, ..., v1.1.0] require amphp/amp ^2.0.3 -> satisfiable by amphp/amp[v2.0.3, ..., v2.6.4]. - vimeo/psalm 6.0.0 requires amphp/amp ^3 -> satisfiable by amphp/amp[v3.0.0, v3.0.1, v3.0.2]. - You can only install one version of a package, so only one of these can be installed: amphp/amp[v2.2.0, ..., v2.6.4, v3.0.0, v3.0.1, v3.0.2].