Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires silverstripe/campaign-admin 3.0.x-dev -> satisfiable by silverstripe/campaign-admin[3.0.x-dev]. - Root composer.json requires silverstripe/installer 6.0.x-dev -> satisfiable by silverstripe/installer[6.0.x-dev]. - silverstripe/campaign-admin 3.0.x-dev requires silverstripe/vendor-plugin ^2 -> satisfiable by silverstripe/vendor-plugin[2.0.0-alpha1, ..., 2.x-dev]. - silverstripe/installer 6.0.x-dev requires silverstripe/vendor-plugin 3.0.x-dev -> satisfiable by silverstripe/vendor-plugin[3.0.x-dev]. - You can only install one version of a package, so only one of these can be installed: silverstripe/vendor-plugin[1.0.0, ..., 1.x-dev, 2.0.0-alpha1, ..., 2.x-dev, 3.0.x-dev, 3.x-dev].