Your requirements could not be resolved to an installable set of packages. Problem 1 - silverstripe/recipe-cms 5.x-dev requires silverstripe/cms 5.x-dev -> satisfiable by silverstripe/cms[5.x-dev] from composer repo (https://repo.packagist.org) but silverstripe/cms is the root package and cannot be modified. See https://getcomposer.org/dep-on-root for details and assistance. - silverstripe/installer 5.x-dev requires silverstripe/recipe-cms 5.x-dev -> satisfiable by silverstripe/recipe-cms[5.x-dev]. - Root composer.json requires silverstripe/installer 5.x-dev -> satisfiable by silverstripe/installer[5.x-dev].